I have to say it will NOT cost you 1000 bucks to run wow.

It did NOT cost me anywhere near that much to run it off my basic computer and I run 5 wow's on one pc. And I only have 4 gigs on XP which only see's 3.4 of those.
And yes at 15 with good grades you can get enough money to afford to run the wow's for a year. As long as you have no other fee's to pay.
I'm going to take a guess by the name and picture you are female.. Take on babysitting. Subway MIGHT take you on. But it depends on your state. Here I would not of been able to hire you do to the utensils that we used. But that is my states laws.

Your best bet to see what your computer can handle is sending yourself trial account offers. Load them adding one at a time. When you notice things are to laggy or notice your computer bogs down. Then you know your computer's limit.

And yes get keyclone. It is IMO the easiest and best software to use.