Things sound as though they are looking up, good for you and him
As an aside, I had a pup, fully immunized that somehow (maybe on a walk?) got parvo, it ended up being an all night thing like you (I had no idea what was wrong) took him to the vet, she gave us (this was like 10 years ago I am trying to remember) some pills or something for him to take, he continously vomited them up, anyway the wench sent me home with him (I had 2 other dobies at the time, one a older pup herself and one adult) -after talking to my cousin a vet tech I realized how serious this was and was able to get him in the next day to a different vet; she told us she was not sure he would make it, they did the IVs and all and he stayed a day or two and did make it, problem was I am firmly convinced the other vet knew damn well what was wrong and did not want to be bothered (I guess there is a lot involved and because it is highly contagious, a lot of work to take of them)- well she sent me home and I guess dobies are particularly at risk of succoming to parvo, and my other one (early because I knew it could happen) although immunized ended up with it too and has just hospitalized for day.
For us the expensive price tag was worth it, the adult dobe never did get it.
I was really confused and ask how they could get it when they were immunized and was told it depended on the amount of "particles" they were immunized versus the amount they were exposed to" don't know if that is true or not but that vet that saved both dogs became our vet for the next 10 years and actually it was a truly wonderful office.
I'll be thinking about you guys, sounds like you have done great so far.