1. Actually, if I recall correctly, Padme was 14, and Anakin was 9, which would make them 24 and 19, respectively, in Attack of the Clones. I can't remember Ben's age, though. Luke and Leia were early 20s, again, I don't remember the exact age they were supposed to be. Sorry.
2. Yup, you are correct. Just chalk it up to Lucas not paying attention when he wrote Revenge of the Sith.
3. Actually, R2 never says he's searching for his former master. It is Luke who suggests this to Ben ("I think he's searching for his former master, but I've never seen such devotion in a droid before.") Due to Revenge of the Sith, we are supposed to believe that, since only 3PO received a mind wipe, that R2 does remember Obi-Wan, and that's the reason he's so eager to complete his mission. And I suppose we're also supposed to assume that Ben is just covering up, but I really don't buy it. It seems kind of weak to me. Your first guess was right. The droids were just put in there for fandom's sake, but it seems a heavy price to pay. They never really seemed to fit in, did they?
4. Yeah, I always pictured it that way, too, before the prequels, but I suppose I can accept this one without too much struggle. This is all part of Ben's attempt to cover up Luke's father's origins "from a certain point of view."
5. Once again, this is just for Luke's benefit. I can't remember who said it here, but it really amused me. It was something like, "What did you want him to tell Luke? 'I nearly killed him and then took his lightsaber from his dying body'?!" There are some people, however, who would consider this a continuity error. I think that's taking it a bit far.
After 5. 6, I suppose, since you had no 6. Yeah, I wish it had all fit too, as I am also a perfectionist. And there are many here who feel the same way, but there really is just no way to reconcile everything that was done in the PT to the OT. It's sad.
7. Hmm, you got me there. There are many people who have read the script/novel, who can answer that one for you.
8. Yes, the point was (although it came across quite unclear in the movie, unless you already knew what Yoda was talking about) Qui-Gon had become the first Jedi to learn how to become one with the Force (ie. become a Force ghost). In a deleted scene or a scene that wasn't shot (I can't remember which), Qui-Gon appears to Yoda and teaches him how to do it, and that's why he tells Obi-Wan to seek him out on Tatooine to also learn this ability. That's why Vader seems so surprised when he kills Obi-Wan because it's something that hasn't happened in recorded history.
Well, I hope this answers your questions, and I hope you have a good time on these boards!