Thanks for reading
Mmm it's a tricky one about the tour; I really wouldn't recommend it for most 7 year olds but it sounds like you have a little imagineer in the making
I think it would drive most kids crazy walking past all the rides and not actually riding them! so with that in mind I would schedule it for the end of your trip when you have riden everything you want to
I'd also sugest the DLP Tour over the Studios for a younger guest as the Studio Tour does spend a fair bit of time taiking about the history of the original Walt Disney Studios in California and the history of film in general
If your little one enjoys learning about the design and stories behind the park I am sure he would enjoy it
I don't think you would have a problem booking a day or two in advance unless it was a very busy time (Disney don't do a great job of advertising it!) you can sign up at your hotel concierge desk if you are staying in a Disney Hotel or at City Hall on Main Street
Another thought; if your little boy wants to design Disney Hotels how about doing your own little tour of the resort hotels? he could take photos of his favourite features in each hotel and make some notes about each theme plus maybe collect resort specific pins at each hotel?
Phew - that answer was longer than my trip report