Anything you need to know about the Mass Effect Universe can be found
here.
Again, standard RTD rules apply. In true Mass Effect fashion, players will get a recharging kinetic barrier to protect them from damage. If you don't get hit for a while, it'll recharge on it's own or certain powers can make it power up faster. Enemies will either have a kinetic barrier, enhanced armor, or no defense at all.
Biotics and tech-users have both pre-assigned skills like Throw, Singularity, and Warp, but don't be afraid to do creative things with biotics and tech. It will be assumed that Adepts and Engineers will have better biotic/tech skill than Infiltrators/Vanguards/Sentinels, and their bonuses reflect this, so go wild and get creative.
Mass Effect 2's ammo system is lame, so everybody is assumed to have infinite ammo, however using a gun too much in rapid succession will cause it to overheat, rendering it useless for a few turns. On the subject of ammo, certain classes will get ammo powers which affect what your shots do. More on that in the classes section.
On skills, ammo-based powers last until you overheat or until 3 turns have passed. I'm going to try to avoid putting exact numbers on most skills because I want rolls to determine most things. For example, if you roll a 1 your Tactical Cloak might screw up and malfunction, making it useless for a few turns. If you roll a 5, it will completely shield you and last for quite a while.
Finally, and very important, your class will start with a single gun of every weapon type they can wield. So a Vanguard will automatically start with a Pistol, an SMG, and a Shotgun, and so on and so forth.
Popular in RTD's nowadays, I won't be using an HP-based system, but instead realistic damage. If you get your leg shot, expect movement penalties. Other than all that, regular RTD thingies apply.