my wife uses a 6870 on a 22" screen (1680x1050) and she plays bfbc2 and aion maxed out. she also has a i7 920, with 6gb mem.
your memory question has more to do with the cpu you choose. if you get a socket 1366 cpu, your get tri channel (sets of 3,6,12,24) or if you get a socket 1156, 1155 you get dual channel (2,4,8). now the amount you need really depends on what you plan on doing with your pc. originally we started my wifes rig with 3gb mem, and everything worked awsome till she started in with aion, and that game would require quite a bit more for the lager battles, so we upgraded her to 6gb and havent had a problem at all. 4gb will most likely be enough, 8gb is more than enough and i doubt youll ever use past 5gb even with 2 games running tabbing back and forth like my wife does.
your cpu is a bit simpler i think. the socket 1156 and 1155 cpus have shown better gaming numbers than the 1366, and is probably still cheaper to build. i havent looked in a while but i think the only think the benches the 1366 still wins in the multi threaded encoding/decoding apps, so if youre just gonna surf the web, play games and other odd tasks then there is no real reason not to get a i7/i5 socket 1155 setup. proven work horse and great oc potential, cause higher clocks mean more performance in games over more cores (4cores vs 6).
so lets say i was in your possition, i would probably get a i7 2600k, 4gb mem (can always add another 4gb kit if you need it), and for a gpu i would get the strongest single card setup possible. this will keep you up to date for a minimum of 2 years, and if you have money left over i would look into a cm hyper 212+, different cases, mouse/keyboard, or any other personal perks.