There are only 2 Teams for this gametype and the maps are fairly large. There are 3 versions of Dominance like Command(like Invasion–but better), Territorial(Just like territories), and Contamination(Infection)
The Red and Blue Team have a Control Center where their armory and vehicles will be. However to make it more fluid there are also Respawn Zones like in Halo Reach (Respawn Zones will depend on author of map). For Objectives the 2 bases will be at the north and south sides of the map and the objectives are in the middle of the map to balance everything out. But what gives a twist to the game is there is a Currency system which will fully be usable throughout the whole game and you will never have to buy it again but you MUST be in the Control Center to buy the items.
Products include:
Weapons
Vehicles
A.A.
Equipment(like Turrets,Barricades,Health Antennas which will heal you when standing next to, etc.)
Soldiers
Fortifications and Upgrades
For Soldiers you can call in any of the following: Spartans, Covenant, and Marines.You also can choose where they will be dropped from the sky but it must be a flat ground. Each soldier has a different price and a limited amount so everyone is not spawning alot of dudes.
Fortifications and Upgrades are perks which can be bought such as improvements for yourself like higher shields or increased speed then for the Control Center perks include shields/defense system for your Control Center.
You get credits by killing people and finishing objectives but you get more depending on your special kill you get like Killing Sprees or Killionare.
You win only by 2 ways: Destroying the enemy Control Center or finish the objectives/capture all the territories.
The Matchmaking Obectives for both the teams can include:
1)Destroy enemy tower(Objective finished when first team destroys enemy’s tower)
2)Capture Neatral Base
3)Capture Intel and return to Control Center
The game will have a time limit leading victory for the team with the most kills and commendations if no other team finishes the objectives or destroys the other team’s Control Centers.
Zombie Mode is where the Blue Team are Flood and only defenders. It’s basically the same thing with the Control Center exept Weapons, Vehicles, and AA’s. However you may not turn into the Flood but your A.I. soldiers will but you do need them for the extra firepower as it will really be needed against the hordes of Flood (Real Life and A.I.) so it’s reccommended to protect them. Flood will have their own perks to buy like wall climbing, faster speed, and other things but only for themself.
For Zombie Mode Objectives:
1)Get a hold of vials and samples from a lab
2)Scavenge parts for the transporter vehicle
3)Wait till vehicle is fully contructed
Now your thinking about having a problem with A.I. in Matchmaking or Custom Games but look at Firefight and plus you can create A.I. Nodes so they set a path they can go(Killing Floor SDK) and they can sense objects so they don’t run into walls.
The game is fully customizable from maps to game variants just like any game variant in Reach for Custom Games.
Objectives will also depend on the author who created the map as they will be able to create their own objectives to the map just hope your friends can balance the map out for the game 
Your thoughts? Plus think of your own objectives I would like to put a list here of some really cool ideas from other people.
EDIT: For some explanations–
Everything has to be balanced. Buying weapons is not going to be that easy. “Now I’m strong” would have already been figured out because your team knows you deserved that weapon cause of the actions you made during the game to help the team win. Powerful weapons arent going to be cheap nothing will. You already need to know what you want to focus your money on even before the game starts. The things you buy will define who you will focus to be as like a “Sniper who buys fortifications for your Control Center.” I mean most gametypes in Halo Reach had to get loadouts especially Invasion where it took time to actually get better loadouts by Phase 3.
Just remember, especially for the kids, they will not get “cool” stuff unless they actually work hard for the team.
It shouldn’t have to lag, I mean the game is going to be very improved and bigger maps will not destroy the game. Look at Battlefield maps those are pretty big but they don’t lag. They can make their maps hold up.
Plus Bungie had a panel of the things they cut like a global battle like map: http://www.youtube.com/watch?v=pZs8ryXP4kE watch at 7:43-8:42
Defense system for the Control Center will all be presets so there will be no Forging. For barricades its different as soon as you buy a barricade from the Control Center just a press of a button on the D-Pad will let you spawn it wherever you want in the map and it will spawn like in halo reach with the halographic animation.
These are some questions answered from other people who posted on this topic