See, I didn't like Florence the first time I went (it was the fourth day of our trip and I think we were getting hit with exhaustion), but I've loved it the past two times.
I understand what you're saying about kids but you're DH has never been before and he's likely to feel overwhelmed (he'll be overwhelmed anyways), but I can't imagine trying to squeeze in Paris and your little village (sorry, I can't remember the name since it's a different post), along with Spain, some of Italy and some of England in such a short span of time. I will say again though that Rick Steve's books are amazing and he has lots of inexpensive hotels on his list. Have your DH read the books and see what his top three things are. Also, I hated spending the night on a train. We did it this past trip from Paris to Florence and at every stop, the four of us (two girls, their mom and me) would wake up and wonder if they were going to put someone else in our cabin made for 6 (even though I still have no idea how they would have fit two more people in there.