Bingo, I like the Geonosis becomes Tatooine idea, at least regarding the first film.

You were asking how would Shmi end up on Tatooine?

Maybe it's a system abandoned by the bad guys of the clone wars and the republic steps in to settle it?

They encourage farmers and such to colonize it and so the Lars family steps up and moves from Geonosis to Tatooine.

It's too bad there's not more footage of a young owen to set up more confrontation between him and anakin over the latter wanting to leave when owen gives him the tantalizing prospect of staying.

Oh man, you could parallel ESB when Yoda encourages Luke to stay and finish his training rather than go help his friends.

You could do something similar with episode 2 where it's owen encouraging anakin to stay on tatooine with his mother and not return to the fight to help a friend(obi-wan captured by dooku).