Well, unless you use it memory is expensive. 4 Gbytes is actually fine for most people. Without knowing the board it is hard to say but it probably has 4 memory slots. Looking at good old overclockers, most memory seems to come in 2 Gb sticks, so if you get 2 off 2 Gb sticks it will do for now and leave (probably) 2 slots free for another 2 in future. What you want to avoid is getting 4 off 1 Gb sticks as this will mean an upgrade requires you to throw at least two away (boards want you to use two channels, the memory slots are colour coded).
As for graphic cards, these are only really useful if you play games. One decent card is enough for most human beings. 'Crossfire' and other schemes allow you to parallel up cards to get higher detail/faster frame rates on BIG monitors. You need two pcie slots on the board for this (board adverts say crossfire enabled and such like).
If you don't play games or have a large monitor one decent card is all you need, and maybe not that if the motherboard has onboard video.
If you do play games an ATI 5770 at ~ £130 is enough. If you don't play games the motherboard may have onboard video anyway. If not a sub-£50 card would do.
Note that a lot of the mainstream gaming cards take up a lot of space and use a lot of power, so fitting two is not always that easy and you better have a good power supply (>500 watts at a guess, real watts too not Chinese !).