1. I haven't played the first and I've played probably just the first act of Diablo II, but a long time ago and I hung on the game play, so yes.
2. If you never played Diablo, go play in single player, then switch to online when you'll know how it works and such... It's always better :P
3. Check your graphics card, as you didn't specify which one it was :/
With what you already gave, you fit in their recommended requirements, though here's a the minimal requirements chart, so you can check if your graphics' card is good enough: