The spindle is the hard part.
Quite a few people use the Tormach system (TTS), which I think is essentially a modified R8 spindle/collet setup.
You could go for a conventional ISO/BT spindle with a drawbar, and attach an airgun for loosening/tightening the drawbar.

Best option is some form of ISO/BT gripper spindle, but they are expensive. I'm sure I've seen ISO30 ATC spindles for around £800, however you need to add a motor to that.
I still have a DaleCNC ISO15 spindle cartridge sat in the workshop doing nothing if you're interested. It cost me about $1200, but I'm open to sensible offers as I've currently got no plans to use it on anything.