Python can be installed in various flavours - I have 2.7, 3.6 and 3.7 installed on my machine in parallel, without further issues. For Ortho4XP, I'd recommend Python 3.7 in a 64 bit flavour - and install it under C:\python37 (it doesn't interfere with Python 2.7).
My Ortho lives on an external HDD (mine is called k:). There, I just created a directory for O4XP to live in. I use 1.30 for quite a while, so I had to fetch it via git. Not sure it's still the case, but it's the only way I know... I use cmder to have a better console than default, and it comes with Git for Windows bundled if you like to...
Furthermore, you'll need a couple of Python libraries which normally require a compiler, but there's a site hosting pre-compiled packages for Windows, which is highly useful: www.lfd.uci.edu/~gohlke/pythonlibs/