How many allowances can I list on my w4 if my wife does not work to stay home w/2 children?

Answer 1

According to the W4 worksheet, you can claim 4 or 5:
A -1, B - 1 (if you have one job), C - 1, D - 2.

Answer 2

That's four for the people, and depending on your income, might be 2 or 4 more for the child tax credits - see the worksheet. Depending on your circumstances, might even be able to claim more, but I'd stop there.