Python is a scripting language. There are scripts that automate everything from turning lights off to creating clothing. IME = In My Experience.

DAZ|Studio can use almost all the content Poser can. Most of the free stuff out there is meant for Mike 3 and Vicky 3, DAZ's figures (because even Poser users who don't use DAZ|Studio use DAZ's figures).

I recommend D|S only because it's free. 3D is not for everyone. Might as well find out if it's for you before you spend a lot of money.

Don't be afraid of Poser 5 and 6. I basically started with Poser 5, and the only thing that's more complicated in P5 than in P4 is the Material Room. Poser 6 fixes that, by letting you use both the P4 and P5 methods for applying materials. You can use the simple version when you're starting out, then switch to the more advanced version when you're ready.