From my prior research, I think there are only state sponsored plans. I ended up going with a New York State 529 Plan, which invests in vanguard and I think has the lowest expenses. (very slight difference - 0.16% for NY v. 0.19% for Nevada). I have read that the NY plan lacks international exposure, something notable if that is important to you. I didn't actually know this when I invested with NY's 529. I was just looking for low expenses.
I really don't know how much to put in, but I'm erring on the side of less. Our 6 & 4 year old currently have around 20K each.
I don't contribute regularly, just when there is something like a bonus or a birthday gift for a kid, or other random extra money, and I just put 50% of the amount in each kid's account. My initial larger investment (just a couple of years ago) wasn't split 50/50, I put slightly more in the older girl's account.
Check your state's tax rules. In PA, I'm lucky that I can deduct contributions to any state's plan from my income for tax purposes.