Yes, you can check-in whenever you arrive, though the earlier it is the less likely your site will be ready. However, when you check in you will get your KTTW card and parking pass so that you can park in the overflow lot and hop a bus, or drive to the parks. BTW, I don't blame you about trying to drive, setup and hit the parks... it's way too much for me, afterall, I'm on VACATION, right?
As for CGs between GA and FW I can recommend one to avoid: Osprey (formerly Vance's). It's got awful bathhouses and is $35 a night! Even with shower shoes I couldn't bring myself to use it... I wouldn't want my towel to touch any of the surfaces in there -- I guess I could have held it in one hand while I lathered with the other!