I like the ideas. For the bodies though I think it should work like you open a category for bodies Then select whatever body type (spartan marine elite flood or whatever they add) and it generates a random armor type and color combination then you could hit a button that creates another random OR creates a copy of the last one so you could make it look like a squad of spartans in the same squad were all killed instead of doing it over and over until you get the right ones.
Also turrets LOTS of them. I love making fortresses or ships with tons of defences, but if I wanted to make a human one I'd have to use the one standard machine gun turret or place a vehicle with a gun and place a bunch of stuff so you could only use the turret and not drive it around. It severely limited its firing range and didnt look nice. With covenant same thing, plasma turret or shade then I'd have to lock up a wraith or revenant or something to use. I think they should add machine gun turrets (but alot of variations like the standard, heavy burst fire, or maybe single fire heavy rounds), Gauss turrets, rocket turrets, Heavy round turrets (shoots scorpion tank shells or something more like artillery), grenade launcher turret, etc. (and they should be a mix of the normal one they have now where it's just on a tripod and you can remove it but then you nly have 200 bullets, and sit in ones where its a like a vehicle you sit in and can shoot, but can't move). For covenant they could have shade turret, fuel rod, beam turrets (like the new covenant sniper maybe a little weaker), new phantom style turret, maybe one that shoots beams like hunters did in halo 3 (also a god mix between removeable and stationary).
Adding those cool floaty scout towers covenant always use in campaign, maybe in different colors, so you could create a litte outpost or a cool entrance with guard towers.
I played a map in reach where someone made a sorta zipline style transportation thing, so adding ziplines would be awesome, maybe even ladders or elevators.
A scarab would be cool (maybe not in forge, but its possible if it's a seperate disk), same with a mac canon or something.
A battery recharger, I always hated how covenant weapons used the batteries that couldn't be reloaded instead you'd need to find a brand new one. Adding a station or somethign to recharge batteries (with set time limits or number of uses so that people wouldn't just camp next to it)
Instead of adding ships, just make good forge maps that are the interior of the ships (sorta like anchor 9 how you're inside a space station, but better for forging)
A new limit system I always had the problem of never having enough of what I needed and WAY too much of random other stuff. I understand why they limit stuff, but I always had to remove cool things I wanted in my map due to lack of space, maybe adjust the budget based on the size of objects not a limit for each category.
Those are a few ideas I have I have more but this is getting too long and boring to keep adding to so I leave the rest to the other members of the Halo community
in my opinion it would work good if they had a great campaign and firefight on disk 1 Have forge, custom games, and Matchmaking on disk 2. and have theatre on both since you'd want videos from both disks it'd be much more convenient.