The Empire Strikes Back/WMG

Dagobah is Naboo.
Naboo: Swampy? Check. Out of the way backwater? Check. Chock-full of strange animals? Check. Good to go! Admittedly, the Gungans are missing, but knowing Palpatine's racism, it would be just like him to kill them all. And it would be easy to miss Theed-it's not that big of a city.

Luke didn't coincidentally find where Yoda was hanging on Dagobah.
Yoda set up camp where he knew Luke would crash.
 * Actually, Yoda used the Force to "help" crashing the ship in that place.
 * R2D2 knew where Yoda was hiding, and steered the ship towards his camp.
 * His beeping when Yoda showed up is something like "Yoda! It's you! We've come for your help!" rather than being started by his sudden appearance.
 * But, wasn't R2's mind wiped at the end of Episode III?
 * Nope, only C3PO's.
 * How much of C-3PO's mind was erased?

Yoda deliberately speaks that way as a teaching method.
Yoda constructs his sentences object-subject-verb. Knights of the Old Republic presents Vandar Tokare, a Jedi Master of the same species, who uses normal grammar, so the rearranged sentence structure is not a feature of their species's language. My theory is that Yoda deliberately rearranges his grammar so that anybody listening to him has to break apart and arrange his words correctly. To do so, they have to listen to what he is saying. If they understand what he says, they will understand what he means.
 * Remember, he didn't have this speech problem talking to Obi Wan's force ghost.
 * Or it could be, y'know, an accent. Tarkin's accent is different from Han's; the Thrawn trilogy confirms that Wookiees can have speech impediments; since nobody knows anything about Yoda's species, we can't confirm whether they have accents or not. It is, however, an interesting idea. (This troper, incidentally, enjoyed restructuring Vandar's sentences to Yodish).
 * "The species' language"? So an entire species has only one language? What's ours? It it Esperanto, amiko?
 * Not to mention, someone as old and wise as Yoda, living among Basic speakers for as long as he has, would have had plenty of time to fix any accent if he wanted to. Whether it's his natural accent or not, he probably kept it for the reason listed above, and because sounding silly and being underestimated because of it makes your points hit home that much harder when you prove them. This is exactly the kind of sneaky manipulative-for-your-own-good stuff that Yoda and Jedi he's trained are known to do throughout both films and the EU.
 * If you pay attention in Knights of the Old Republic, you'll notice that Vandar has the habit of blinking his eyes sequentially. Perhaps each member of his and Yoda's species are born with their own unique quirk? Vandar's quirk is his blinking, and Yoda's quirk is his speech pattern.
 * I saw a special on the original trilogy once in which the cast said (although it may have been their own speculations and not straight from Lucas and the other powers that be: they weren't clear on that) centuries ago, back when Yoda was young, everyone talked like him (or at least where he was from). Languages evolve over time, and the one represented to us as English when we see the films got its subject-object verb order rules changed as it did so, yet he just kept on talking the old way--be it out of force of habit or nostalgia or tradition or fear of change or heavens knows what they didn't say.
 * In the prequels, Yoda is seen teaching the younglings. The sentence construction could just be a way to make his teachings more memorable. After all, 900 years is plenty of time to get good at memetics.
 * This theory is actually pointed out and discussed in-universe by Luke and Ben Skywalker in the Fate of the Jedi series.
 * Latin has a tendency to put the verb at the end of the sentence, and as verb conjugation includes an implied pronoun, it sometimes puts the subject at the end as well. Yoda may be speaking a much older and more structured and formal dialect of Basic, switching only when immediate precision is necessary.

Admiral Ozzel was a Rebel double agent.
What Vader saw as Ozzel's incompetence was actually Ozzel deliberately sabotaging the Imperial war effort. When Piett found evidence of the Rebel base on Hoth, Ozzel dismissed it and tried to dissuade Vader from searching because he didn't want the Rebels to be discovered. Then, with Vader breathing down his neck, Ozzel had no way to warn the Rebels of the impending attack other than ordering the fleet to come out of hyperspace close enough to the system that they would be detected.
 * I hate to say it, but this makes sense. In fact, Ozzel would be perfect as a double agent: who would expect this guy to work for the Rebels?

Admiral Ozzel was also an officer on the first Death Star and sucks at hyperspace.
Ozzel was also an officer on the first Death Star and responsible for coming out of hyperspace on the opposite side of the planet, allowing the Rebels time to launch an offensive. He either is a terrible strategist on selecting where to emerge into space, or is completely inept about popping out where ordered. Either way, his last failure was far from his first.
 * Or, if you believe the theory mentioned above, he was a Rebel double-agent, and did so that the Rebels could prepare and launch their assault. Which would also explain why he survived the Death Star's explosion: he was one of those nervous officers who decided to flee, and probably did so the second he heard that one guy make the comment to Tarkin about preparing to evacuate "just in case".

General Rieekan is an Imperial agent.
General Rieekan’s defense did suspiciously little to stop the Empire’s forces, if not for the improvised tow cables the snowspeeders would have been completely useless. Rieekan’s original plan wouldn’t have stopped a single walker! Rebels were discovered on Hoth, Echo Base destroyed, and the rebellion routed – just as planned.
 * Alternatively, Crix Madine may have had something to do with it. He defected to the Rebellion between Episodes IV and V, but you never know how sincere he actually was.
 * Where was Crix Madine during the battle for Hoth? Certainly not anywhere near Echo Base.

The end scene
It's been mentioned elsewhere that Lando is wearing Han's clothes at the end of Empire. This troper believes he knows why- Lando didn't have time to pack before the evacuation of Cloud City so the only clean clothes available to him are the ones in Han's quarters on the Millenium Falcon.

The asteroid field is the remains of a planet.
There are actually hundreds of those space slugs. They're sort of a species of geological parasite that incubates in the warm cores of planets until they reach full size, and the tectonic plate disruption of their simultaneous maturity is enough to rip the planet to shreds.
 * Even better: it's the remains of Alderaan. The space slugs never bothered anyone before until their planet was blown apart (they, being Made of Iron, survived when nothing else could). That's why Leia is as surprised as anyone to discover they're inside the mouth of one.

Vader's You Have Failed Me tendencies are largely limited to this period.
While EU material immediately latched onto Vader acting like a heartless overlord to his underlings all the time, both A New Hope and Return of the Jedi don't really show him acting that bad to Imperial officers. He Force chokes Motti on the Death Star, but that's because he was showing severe disrespect for him and his powers, and Vader's reaction is to powerfully taunt him rather than get angry. Notice how casually he stops when ordered by Tarkin.

He's unforgiving and ruthless in ESB is because he's desperate to find Luke and gets angry at anyone who hampers that search. Following Luke's escape into hyperspace Vader simply walks by Piett without a word, demonstrating he doesn't care enough about the Imperial's failure to catch the Falcon to even reprimand him. With Luke already rejecting him, there's not much point to getting upset with any of his officers about it.

Chances are Vader's tenure in the Empire probably resembled what it was on the first Death Star. An intimidating figure to be sure, and one not above being remarkably cruel to his enemies, but likely not the Bad Boss killing his own men at the snap of a finger like he was here.
 * One of the best WMGs I've ever read.
 * It is likely that he is indeed angry when choking Motti - if you listen carefully you can hear his mechanical breathing get more rapid, and he doesn't show any signs of letting go before Tarkin orders him to. He probably has a notorious temper in general, but I do think you are right that it peaks during this period.
 * This fits in with the film's opening prologue, which mentions that Vader is "obsessed with finding young Skywalker". And, previously, he'd been obesessed with finding a way to save Padme and, years later, with finding the Death Star plans. Basically, you'll probably be alright as long as you don't get between Vader and his all-consuming goals.

Leia knew she was Luke's sister all along.
She only kissed him to make Han jealous. There has never been any sexual tension between the two, ever. It does not exist. There was certainly never any indication they were originally going to become a couple and the Separated At Birth twist was a huge Retcon. It was all according to GL's master plan.

The reason the Millennium Falcon was acting weird...
It was jealous of Leia.
 * Maybe the falcon is related to Christine.