So I'm looking to eventually get a cage in a future track car build and a 'extreme street' build when my two projects are done and though I might try my hand at welding it myself. I have a friend that can teach me the basics of welding cages, but would like some info on some issues. I have a friend with a homemade roll cage in a Superbird and it had badly aligned doors that would not shut properly. He decided to that the cage was a pain due to the way the previous owner put it in, decided to cut it out. After removing the cage, the door alignment issue they had went away and now shuts properly. I want to avoid some of these problems and looking for some advice.

Should cages be welded with drivetrains in them?
Does the car need to be planted on all four corners or supported on jacks/lift?
Will having all the suspension done first affect the geometry or not an issue?
Steel vs chromoly?

Thanks for any info you have.