Python/CMake/Env build option refresh

[mdavis36]

Yeah I'd like to come back to this specifically at some point and enforce the defaults purely in CMake where we can. I think there needs to be some more standardization/ consistency between environment and build option naming too. (tagging w/ an issue)

The default here of 0 is a little clunky, I'll update just this option to use a None check for this PR.

Originally posted by @mdavis36 in #5740 (comment)