They will run fine, buddy. Despite the drastic changes in the interface, most modern programs will run fine on Windows 8 and I'm certain that you can run Steam and your Steam games just fine. Tom's did benchmarks of games on Windows 8 a while back, and they did have some problems but it was mostly attributed to drivers, which would have been solved by now.
It should be no problem. They have repeatedly stated that backwards compatibility is not an issue. The whole total war series after rome runs fine on win7 64bit so I cant imagine why win 8 would be a problem.
Actually, some games won't work. Medieval 2 Total War will not play on Windows 8 unless it is downloaded from Steam, which sucks because I refuse to pay for it again. Empire Total War will play when downloaded from Steam but it constantly crashes. I don't know about the disc.