Sounds like things are on the right track. This passion he's showing is teh most important!
I'd encourage you to make sure he develops athletically as much as tennis wise at this point. So I think you are spending enough time on the court and I like that there's a focus on technique/fundementals. Add to this, soccer or ice hockey or some other sport that requires a lot of explosive movement and builds him athletically and also keeps him fresh on the court.
When he does start to compete, make sure to focus on just that...competing. And doing it with full effort and full respect. Rather than winning. And also look for him to try and play 'right'...meaning good technique and avoid investing time in strategies that will get short term wins, such as 'moonballing', which you will see a lot of at young ages.
Also...you'll get different advice on this. But I'd keep him in shorter rackets using a smaller court and green dot balls. Or just very used balls. These balls are slower and don't bounce as high and are better for learning proper technique with such young children.
Lastly, educate yourself a little on good technique...there are a lot of internet resources that will analyze the worlds best players and their technique. Make sure the instructors that work with you son seems to be pushing him in this direction.
I love your attitude: "We don't mind if he changes his mind or fails at it, but we would hate to be the reason he didn't succeed." Remember that and you will do great! Support him and his passion but as you get down the road, make sure it's always him and he doesn't feel trapped.