COnverting from VBScript to python

Your question is not that clear to me ...

But if your problem is referring one unit from other (say one script from the other) 

you have to refer this and this

if you need to refer external python libraries (like request, json etc..)

you have to physically place those in <TestComplete>\Bin\Extensions\Python\Python36\Lib folder 

and use "import command"  for more please refer this

QUESTION 1: Do I need to set any of the python env variables like PYTHONPATH when using the TestComplete python IDE and execution?

Answer:  No TC use python installation in your <TestComplete>\Bin\Extensions\Python folder even though you have other python installation in your machine.

QUESTION 2: How do I use sys.path.append for so that the .py tests can correctly import given my folder structure?

Answer: as far as I know you can not. you have to place those files in TC define folders...please refer my first comment.