Ya know, while I think this is a great idea and applaud it, I can't help but point out that your request for players not to "surprise the gm" is perhaps unreasonable. From everything that i've played, DnD to 40k, with bits of paranoia, ruining the GMs plot is an integral part of the experience. Far be it from me to tell you how to run your sessions, but it seems to be taking the fun out of it no? Besides, how would you know what rules you REALLY need if you're not going to let the players experiment?
Oh you can still derail the plot PLENTY. That's perfectly fine. But the game mechanics, you can't try to surprise with.
Let me give you an example. In Pathfinder, there's a feat you can take called "crusader's flurry" If you're a cleric and your god has a preferred weapon, and you're ALSO a monk who has flurry of blows for rapid attacks, then you can make a flurry of blows using that weapon - normally it must be unarmed. So instead of a series of 6 punches in a round, the monk-cleric could make 6 greatsword swings in a round.
In my game, if you try to just do that, and then the first round of combat you say "I use flurry of greatsword" I'm going to say "It doesn't work that way in homebrew." But if you talk with me ahead of time and ASK if the game mechanics allow it, then we can avoid this problem. If you still want to be a weird character and like, use the sewer entrance instead of the skylight, then THAT is perfectly fine. It's mainly just that when you're building your character or your weapons, to double check that I'll allow it. Just don't assume you can put a railgun on your motorcycle simply because the rules don't forbid it...
As for the item specifics, 4th ed gives basically none. Vehicles may list their top speed, but don't list occupancy limit or anything, EVEN THOUGH there's vehicles mods you can install to double the occupancy limit. It just doesn't tell you things, and will have descriptions like "The superpat rocket is a sophisticated guided munition" and then list its damage, range, and accuracy. You can judge by the damage if it's supposed to be a vehicular weapon, but if it's 'sophisticated' then is it a really expensive handheld launcher? It just doesn't say...