The most important thing is getting a good CPU and the trick with RAM is to get as much as you can afford into the first two slots only, that way you can add more RAM to the empty slots without tossing sticks you already paid for, like ideally you want to upgrade by adding shit rather than swapping shit, I would also recommend a second internal hard drive just for audio but you can add that later, for now just get the best CPU you can afford.
P.S. you can also use onboard graphics to cut the initial cost down and add that later if you want and I definitely recommend having a decent graphics card, I usually go for shit which doesn't have a noisy fan on it....speaking of fans bigger is better because they can move more air at lover revolutions, like if your power supply has a big fan rather than a small one it's going to be quieter....no fan is better but you absolutely need to keep your shit cool.