Check out [url]www.theforce.net[/url]
They've got a whole forum about Ep. 3
As far as your questions, here's my $.02:
1. I think Padme's death will be accidental. I can't see Anakin doing it on purpose. It may come from an attack gone wrong, or she was in the wrong place at the wrong time, etc. If you will notice from Ep. 2, Jimmy Smit's character is Senator Bail Organa of Alederaan. In Ep. 4 (A New Hope) Leia is Princess Leia Organa. Maybe Padme flees the crumbling empire with Bail Organa and Anakin thinks Leia is their (Bail and Padme's) daughter.
If you remember from the original trilogy, Leia and Luke are talking about their "mothers", and Luke says he has no memory of his. Leia says she remembers hers as being very beautiful, but dying when she (Leia) was very young. Padme therefore lives for a while after the birth. Maybe she doesn't die in Ep. 3 at all, and George leaves it up to our imaginations (cancer, car wreck, etc.? ha!). I hope not. I would like to know what happens to her. He (Anakin/Vader) obviously doesn't know she (Leia) is his, and has no knowledge of Luke's existence till Ep. 4.
2. I think Yoda flees to Dagobah to hide. Perhaps he is pursued by some evil Jedi (Dooku, etc.) and he defeats them in that cave Luke went in in the Empire Strikes Back. Maybe that is why it is evil and/or why they cannot detect Yoda's presence. All the life readings on the planet could contribute to the inability of the Sith to find Yoda also.
As far as the Obi Wan on Tatooine deal, I 'heard' that when they were filming the desert stuff for Ep. 1 that they shot an additional scene of a cloaked Obi Wan carrying a bundle to the Lars Homestead. Lucas said that way they wouldn't have to come back to film a desert scene for Ep. 3. My guess is that Padme flees with Bail Organa as above, and Obi Wan flees with young Luke and takes him to Tatooine to Owen and Beru Lars (Uncle Owen and Aunt Beru), and the wanders into the desert to set-up a homestead and keep a watch on the growing boy, as well as hide from the Empire.
3. I have 'heard' that Han may be introduced as a young Corellian cabin-boy. Who knows about Chewy.
This is just my guessing /opinion. Take it for what it's worth.
P.S. - I ran spell checker and "Tatooine" and "Corellian" are both in the digital dictionary here at ARFCOM. Scary how SW has infiltrated society, huh?