Grenades are like RAM, you can never have too much
Okay,
You need to buy halo PC, its 20 bucks.
There are dedicated groups in vanilla that do alot of 4v4.
Online halo 1 is only on pc.
"modders" depends on your definition, if you mean what xbox kiddies call modders, then yes, if you mean the proper definition, then no,
Halo PC has about 30% of servers with things like unlimited rockets, no guns warthog wars and eight tanks on bloodgulch. but there are still alot of vanilla players.
And halo Custom edition has custom maps, that allow things like new playermodels,levels,vehicles and weapons, its entirely your choice to download these custom maps though. (they are pretty cool, do a youtube search on "coldsnap" and "hugeass" to get an idea)
...Reach is -blam!-