My daughter will be 16 soon. I have been the sole supporter her entire life. I did not pursue child support. Is it too late?

In Wisconsin, child support is prospective only - you can't go to court and ask for past support (unless, of course, there was already a standing order for child support that wasn't being paid). You could certainly start an action now to get child support for the next two years though. If your daughter is his only child then there's a statutory presumption that he can contribute 17% of his gross income to her support (the formula changes depending on the number of children and their placement situation).
Placement and support are legally separate issues. Unless the father is demanding contact with the daughter, no, your daughter doesn't have to have any contact.

The dad does have a support obligation. He's gotten off easy so far, but that doesn't mean you have no rights to get support moving forward. Contact the Milwaukee County Dept of Child Support Enforcement at 414-278-5160 and talk to them about getting a child support order. You can also contact an attorney to handle this for you if you want.

Raising a kid is expensive, so much credit to you for having done it yourself.