As there's many programmers on here already (and quite a few of them have more experience than me) I'll go for 2d Art as well, UI and HUD work, if you want me to.

Around 2-6 hours per week.

I'm surprised at how many people know multiplayer here, considering the only MP game I know of that ever got to a release state was Glider.
I'd also do MP programming if it's needed, but I understand we've settled for a single player game for now.