How much experience is required to level up?

http://www.steamgifts.com/discussion/XaCbA/list-of-all-cv-levels-and-their-corresponding-real-cv

Also check the FAQ for the value of bundled games et cetera. If you gift something check http://www.sgtools.tk/sent/tream2001 to know the CV you've got.

1 billion

View attached image.

You need 50 experience to get to level 2 and that's as much as killing 5 rats (might be a little hard, depending on where you live).