Setbacks are normal after surgery, neutering, illness, or any kind of changes in routine. I would just keep up with his potty training, taking him out often or taken to a pee pad often. If you are using pads and he does #2 on the floor, tell him NO firmly and take him to his pad. Maybe even put it on his pad to remind him where to go. If he is outside trained, take him immediately outside. He will soon get it again.
As for getting another, I was the same way! I got Jackson a year after Jake. That seemed like really good timing for us, as Jake was fully trained and not having accidents. But, when you feel you are ready for the extra work of training another and taking care of two, go for it! I have never regretted it for a second! I want to get a third...a girl this time! lol
Good luck!