It sounds like you've got quite the excellent young musician on your hands and it's excellent that you are working hard to find what will work best for him rather than forcing him into some strict regimen which might well squash his initial enthusiasm. There's lots of time for the technical drill stuff later as he wants to play more technically challenging music. But you should try to find a teacher who you get good recommendations for from other parents with young musicians in order to ensure that his trumpet playing now on the easier stuff won't develop bad habits which will throw a brick wall in the path of his progress. Talking to pros can help but professional musicians aren't always the best teachers, so talk to other parents of young musicians and try to get recommendations that way. Not all teachers are good with young musicians, so you can't just call a name out of the phone book without doing research first.