Ps4 uses UStream now as well so they must have the infrastructure behind the scenes well under control.
Just search ps4 and you will see at least one stream of drunks and one of a guy sitting alone
Some of the hd webcams these days are pretty good but google is your friend when it comes to reviews.
And it depends if you want wide shots, close ups etc
Yup, I used ustream. As for good webcam, it's like WebbyNZ said, best to check out reviews online - there's always something new out there.
Anything for around $100 will be really good quality as far as I could tell, when I researched last year. I use/have a cheaper one. It's not HD but it works.