Hello fellow PC gamers! I'm finally making the switch, but need some advice.

I'm being gifted a prebuilt rig from an old job I consulted at for a while. It's an HP EliteDesk 800G2 Tower (its huge!), Core i7-6700, 4gb Ram (DDR4-2133). Intel internal graphics (yuck?), and no hard drive (security reasons).

My questions are two-fold. I've been out of the PC Game for a while, and the first thing I'd wanna do is get a video card. Upon research this computer uses the Intel Q170 chipset, with a PCI x16 (x4), so i could throw a video card in. I don't know if the supplied wattage of the PSU (400W) would be enough for a mid-tier / lower high tier video card. I'm sure cooling would be a concern as well.

Any suggestions? I plan on playing Cities:Skyline, Carmageddon, CARS and Trains Simulator.