He'll definitely spray, but if he's an indoor and outdoor cat, you'll have a much better chance that he'll confine his spraying to his outdoor territory. He
will be territorial.
I don't think there's any reason to expect an increase in aggression toward humans
But intact male cats are famous for picking knock-down-drag-out fights with each other, and cats are famous for getting gnarly battle wounds from fighting each other, so it might not hurt to keep a basic first aid kit on hand...for him. I'd say gauze and hydrogen peroxide at a bare minimum.
Intact male cats are just a touch more "wild" (for lack of a better term - the line between domestic and feral with cats is very thin) and a lot of the problems that people have with them stem from expecting an intact cat to be happy confined indoors. He's going to want to establish a territory, defend it, kill the rodents, and woo the ladies
He'll likely still be a good cat and very friendly with his people
---------- Post added at 02:12 PM ---------- Previous post was at 02:10 PM ----------
As for his size, intact cats (aided by testosterone) tend to develop *bulk*. So he may pack on more muscle if he's not quite done developing.