What are good ambient temperatures?

[Homebody]

I'm preparing for my first ball python and I'm worried about temperatures.
Right now I'm running tests on a 4x2x2 enclosure, I'm using an 80w DHP and the basking spot is around 91ºF, while the ambient temp is 83ºF on the hot side and 75ºF on the cold side.
Is this too cold? Should I add a 150w CHE to the cold side?

I think 75F is o.k., but it's right on the edge of too cool. You should keep a close eye on it. You don't have any wiggle room. Personally, I'd add the CHE, or heat tape if your enclosure is made of pvc. It will give you more control over your enclosure temps.