Personally, I don't suggest Demon Hunter.
I'm in the beta and have been hanging out with a clan that's been playing quite a bit. One thing I'll say is that every person I've talked to has a different feeling about the classes, so it's worth trying all of them before committing to playing one.
After playing them all to the beta's level cap, which is 13, there isn't a class that I didn't like. Demon Hunter has some very fun mobility and snare abilities, and I found myself really fascinated by it.
Here's a video of me playing around with dropping caltrops on the ground and using rapid fire to take down snared creatures kited through the snare. Note, this isn't challenging, but with some practice I could imagine doing this in much more dangerous scenarios.
http://youtu.be/a_-LbqQ8zuE
Anyway, while I'm usually playing on a windows PC, I have played the game on my i7 Macbook Air and it works pretty well. I haven't been this excited about a game in a long time -- it's a lot of fun.
And also, I read somewhere that they will include an option to pay for certain things, with real-life money. Is this true?
Yes and no. What they are doing is setting up two auction houses, one using gold as currency and one using real money, so players can sell in-game items to each other for real money. Blizzard, however, won't be selling items to players directly. They will take a cut if and when someone decides to cash money out of their account (though players can use money in their account to pay for other Blizzard products and subscription fees without incurring that fee.)
What this means is that they're not adding NEW powerful items to the world -- instead, rare items are always ultimately from player drops. So yeah, someone could get one of those rare items by paying real money, just as they could if they met the other player in game, handed over the item, and then sent them money by PayPal in real life.
The reason Blizzard's doing this is that D2 had a lot of real money trading around it, and at least by setting up their own auction house, they can do a few things like escrow the item being auctioned, verify that the item is exactly what it's represented to be, and have the logs and information to address any problems with the process by restoring items or money to players' accounts. It's pretty much just to make the whole process safer, on the principle that it's going to happen anyway given how D3's item system works (and the existence of extremely rare items in the game that people are going to want to sell for cash.)