Well we're back from the vet.
I was right about the age and gender!
We have a boy who's now about 4 weeks of age (so about 3 weeks when we found him), and he weighs 10 ounces (he certainly didn't when we first got him!).

He loves my daughter who turns a year old on May first, and she loves him too.

Oh, so in 4 weeks he's getting shots and lukemia testing done, and at 4 months old we're getting him neutered.

I'm going to be getting a fecal sample soon to check for internal parasites.

They were all very happy with me and impressed that I had actually done a bit of research so I wasn't a total 'tard.