Since most of the folks above have answered all of your questions, here's a bit of advice for building/playing EDH.
Build your deck with a bit more mana at first. I'd start with around 40, which can be reduced based on your ramp/artifact mana.
Put in whatever cards you want. Don't rely on lists of staples or top ten lists. Sure, if you want to add those cards, then great. What I'm saying is that you should enjoy playing your deck, and sometimes if it's choked with must-use cards, it can feel a bit generic.
The best way to figure out what cards you should add or subtract is by playing EDH a lot. This should go without saying, but many of my friends get so caught up in construction that they're reluctant to play their new deck because they're not sure it'll work. Just play, and any time you see a card in your hand that you just can't use, cut it! When someone plays a card in your colors that you've never seen before and it's awesome, buy one!
Lastly, play a lot and have fun. That's the reason we like this format, right?
-Phrank