filphil, I really don't see a point of any resolution smaller than 1080p anymore. 21" 1080p monitor only cost $100. But like you said, OP might have old already.
The most important thing OP has to look for as a budget gamer is to look at the performance vs money ratio. You always has to pay double or more money for 5-10% gain for top end hardware, which it is really not healthy for budget-conscious gamers. The best is to look down 1-2 tier lower.
SLI, crossfire or watercooling are for hardcore hardware people. Usually by the time you have enough money to get a second card, there are already better single card solution out there for the same cost. And then there are game compatibility problem with SLI or CF mode. Watercooling is an expensive hobby, you are always better off to just buy better hardware than the little performance you can gain from water cooling.
As for soundcard, unless you have the speakers and ears to back it up, there is not much advantage to get a dedicated sound card anymore. And I used to be an advocate of sound cards. Onboard soundcards are just doing a good enough job nowadays.