The vehicles already have a lot of vehicle specific variation and "passive" traits, like the armor that can be chosen, it's thickness or protection and the actual area it covers. There's also vehicle speed and acceleration and, turret height (IFVs have a high turret that gives them the advantage of using more objects as cover while not being completely blocked). That all being said I would personally go with option 2. The choice of an autoloader is a great idea. I've thought of a few more abilities to get us started. A radar like the one for the UGVs that detects enemy movement around the vehicle taking up the APS/jammer slot. Instead of several smoke grenades the option of fewer thermite or incendiary to burn infantry and damage components of vehicles (unsure of how that should be aimed if aimed at all). Lastly some sort mine protection whether it be showing them or just extra protection against them.