Should I charge anything when rehoming this dog?

I think you're justified in asking for the amount you paid for neutering and vaccinations as an adoption fee. It will weed out crazies, hoarders, and people who buy for labs and fighting bait dogs. If the thought of taking money bothers you, donate the fee to a local rescue to help other dogs. I also think you should feel comfortable asking for a vet reference from potential new owners and asking to visit their home and meet any other pets. You put alot of work into this boy and want to make sure he gets the best possible home, so don't feel bad about being picky.