I can help you making a great gamemode with other child modes inside, I mean, Team Death Match and Search & Destroy, like a mmofps based on gta engine.
Examples:
http://crossfire.z8games.com
Or you can continue my old project, "CrazyTaxi", it's a great simulator which is using peds as fares and sqlLite as DB.(i closed it due to high numbers of bugs), it a also has vehicle-system, with handbrake etc etc...