It still might be a bit much if all you need to do is record your voice and a piano. That should only require 2, maybe 4 tracks at the most (each instrument / voice on the recording takes up one track. Sorry if I'm stating the obvious). Were there any other instuments or voices you wanted to record? If so, then an 8-track might be worthwhile . . . or 12 if you want to record a lot of extra voices/instruments. And you'll want a decent preamp.
If you have the extra money, Ametth did have some good suggestions (joking aside, and with all due respect to his knowlege of computer hardware) although they might be riskier should you decide that recording on a more serious level isn't your bag.
Good luck.