Drop me an e-mail and I'll send you a couple of snaps of our CRX race car cage install. We are set up for both Improved Touring and Honda Challenge and the car is gutted. How to paint cage-my fabricator, after welding, used Rustoleum in a spray can-looks good and is easily touched up as needed. Just mask off everything you do not want painted this way. Use some pieces of cardboard as shields too. Our cage is a KIRK and custom welded in.
If you want to have the interior in the car-that can be done, but the preparation is a real pain-you will need fire blankets to protect from the welding. Another thing-when buying the cage specify whether the car will be gutted or not and What class you plan to run-roadrace or autocross or drag for that matter.