Is a Cadillac deville a good first car ?

That is a junkyard refugee. Even if you were skilled at working on cars, I'd still warn you to walk away. Cadillacs have so much automatic and redundant, complicated stuff that fixing simple things are no joy, knuckle-busting and expensive. They drink gas and aren't all that reliable. Instead, look at a Lexus or Camry with 84,000 miles or less and enjoy it for years and years.

This car will drink gas like there is no tomorrow. And not too many mechanics will know how to work on it because their scan tool will not work. No.

The car you mention is probably not very reliable and given that it goes back to 1994, very old and hard to get repaired if need be.

A better first car would be a Honda.

A 23-year old car? Cadillac or any other, that's an old car. But hey, if that's your dream car, go for it.