If I'm going to buy a game from US..

[Jdevil3]

I think the only game that is region locked is Persona 4 Arena, so as long as you don't buy that one you'll be fine. You can buy any game you want except that one.

As for DLC, you can create a US account, buy a US PSN card to add funds to your US PSN account and buy the DLC you want from there. You can even buy the DLC with your US account and play it with your real account if you want... at least most of the times. I think there are a few exceptions here and there where you had to play the DLC with the account you used to buy it but I don't really remember.