The optimum Dynamic website CMS (AS3+XML+PHP+MySQL)+resolution

I would like to try to build a big site - something like facebook (:hugegrin:) but in flash.

*What is the optimal resolution for this mission?
This is very critical, 'cause i’ll build the whole site(s) at this resolution, and a mistake is a big damage.

*I’m planning to do the integration like that:
Flash AS3.0[SIZE=1][COLOR=blue]—XML—>[/COLOR][/SIZE]PHP[SIZE=1][COLOR=blue]—SQL—>[/COLOR][/SIZE]MySQL[SIZE=1][COLOR=blue]—Data—>[/COLOR][/SIZE][COLOR=black]PHP[SIZE=1][COLOR=blue]—XML—>[/COLOR][/SIZE]Flash AS3.0[/COLOR]
Somone can give me several advices?
This is my first time of doing this integration.

*What classes should I pay attention for?

*I want to apply the aforementioned integration for anything:
Login the user, read messages etc.
I think the “loyal” way to transfer data is with XML,
but for a short and simple (username and password only) Login- maybe in fact the best way is GET method? or still XML?
I heard the best way is to create one function for the Integration-how do u think to do it?
Don’t answer my whole question- any piece of information will be useful.

I think this Thread will be very useful for many users,
hope to hear u!

P.S. I’m new here, and I’m from Israel.
English is not my native tongue,
so if I have a critical grammar mistake do not laugh and tell me.
I write here because this seems like a professional forum, and I’ll improve my English.