You certainly can use your time better then checking all day for responses. Why not check-out the Wiki or perhaps read Vyndree's Guide to Guides. Many beginner question are answered there instead of someone having to re-type the same answers all over again. Another good page - Getting Started

As to answer your questions:

1. Since you give no system specs, here are some possibilities: a 486 DX4 100MHz with 8 MB of Ram and a 1 MB graphics card will not run 3 instances of wow, neither you can run 3 instances of wow in sunfire server, unless of course you want to fiddle with wine, can be fun if you have wine along with if
I would a recent intel or AMD processor (no more then a couple years old) with a at least 2 GB of Ram and a decent 3d card, nvidia 8600 (or equivalent ATI) and up, you should be good. Here is what you can do - create a couple trial accounts and try it out!

2. If you playing one computer, WoW doesn't really care if you are wireless or not. For multiple computers, you better do some research