[glorious bulge]

solution F: (my favorite) allow the jetpack to slow fall but not boost high

This is pretty good, because you can't really stop people from going into the ceiling as long as the jetpack has boost. you have your normal jump, but then the boost as well. You could make it so that as long as you're holding space, your gravity is lowered a bit. That helps the slow fall and still allows a bit of a glide, like the boost offers, without being able to increase your effective jump height past whatever the server wants it limited at.

On the jetpack being free or whatever, I do think new players should at least have access, if not having it equipped by default. You want new players to feel how "the server's supposed to feel." There will be stupid players, but I think if the movement feels good on the server, it may lessen that somewhat. Also, new people aren't going to immediately know to go in and equip it for the game to feel right and most people hate default movement for TTT on these big maps.