ICOT: Whether or not memory needs to be installed in pairs depends on the system not just the memory itself. However, almost all memory sold today is DDR (double data rate) which is much faster (there’s a formula for calculating how much but I forget) than older modes but only if installed in pairs.
Mod-80: That means adding that one 2GB chip would speed your computer up very noticeably. The $25 would be well spent.
Health:
1- You don’t need a workhorse model, a cheap PC will do fine.
2- Unless you buy a bundled deal like the ones Dell offers, you may end up paying as much as $250-350 for a decent display. Keep your old keyboard and mouse unless they’re broken, replacing would be a waste of $30.
3- Especially since you can get questions answered free in the coffeeroom. 🙂
4- Why not? They are usually very good, often better than their non-free counterparts.