Firstly, he will probably be fine,. our cham used to get spooked when we went near him after initially acquiring him and being so young wasn't too steady on his feet, and did have a couple of minor falls from the branches. Keep a close eye on him and if there are any signs that he is not using his legs properly get him straight to the vet.
Chams are pretty unforgiving of any housing mistakes, and you are making one very big one - the cham isn't getting any UV through the window, unless you have it open. UVB doesn't penetrate glass, and although he may like the heat and the light where he basks he isn't getting any benefits from it. You need to get him a UVB tube or bulb for his cage, or on nice days you can try him outside in his screen cage. Be careful not to allow him to get too high levels of UVB though.. chams live where it is shady and require lower levels of UVB.
As for having a free-roaming cham, sounds pretty cool

but I would keep him in the screen cage when you are not there to supervise.