No, ask long as you have a controlled UTH a basking light is not necessary as Ball Pythons do not bask, they just need belly heat.
This is a thermostat I would reccomend for your UTH:
http://www.reptilebasics.com/product...cat=250&page=1
And here is a very good temp gun I would reccomend for reading the surface temps in your BP's enclosure:
http://tempgun.com/
For humidity I don't think you need anything more than of of those cheap stick on ones to measure the ambient humidity of the enclosure. As long as its 50% or more you're good to go.
I also would not recommend a 75 gallon tank for any BP. the shear size of it would intimidate your BP and most likely stress it out.
Also I am personally against housing Ball Pythons together in a single enclosure because usually at least one of them will try to establish dominance and stress out the others.
BP's are solitary snakes and I strongly believe they have a better quality of life housed alone.