1. Something recent, like a G41-based or P43-based motherboard. Whatever suits your budget, and go with a mainstream brand. No need to splurge if you're not O/Cing. Something like
this would be my preference.
2. 4870 1GB is quite cheap nowadays, or a GTX260; both around $160 before tax. Both will handle new games OK if you're not expecting extreme performance or have a huge screen.
4870 1GB and
GTX260-Core216.
3. Not necessarily.