Looking at a 02 tomorrow. Common problems?

I am looking at the short version of a 02 Escalade tomorrow. I used the search function and did not come up with anything other than certain problems people had. I am not new to forums and will be around here for a long time if all goes well tomorrow. He says the transfercase leaks and he stopped using it and hasnt moved since. Is there a rebuild kit or can I swap one in from any tahoe or yukon? What does a used one go for if its trashed and I need to replace it. More importantly what are the common issues to look for when I go look. My buddy has one of the EXT ones and he likes it. I am worried about the air ride if it goes out, how expensive of a fix is this for the air bags and compressor? Any aftermarket companies that make good parts for a fraction of the cost? Also wondering if the air ride does go out in the back and its extremely expensive to fix, can't you just use shocks that would fit the tahoe and yukon? Obviously the sensors would be on but is there a bypass?
Thanks guys, hope to be here for a while!
Jeff