You need to start with an understanding of a basic signal path and routing in a subtractive synth. lfo - vco, filter, envelope, vca
Another type of setup would be additive, look up those concepts, read about them:
Subtractive, additive, wavetables, granular and wave slicing methods, Physical modeling, AM, FM, TZFM,,,,,read, listen, think and learn.
I have never asked for advice on what modules to get and I will not offer it either. With your basic understanding of the signal flow, you then read about and listen to all the modules available at a given moment.
Compare sound, functions, ease or difficulty in operating them and ask youself, will they give you the result you are hearing or want to hear. Since you are going DIY you can afford to get a relatively stronger setup.
The rule is, don't look for complicating your setup, find out which are the building blocks of a functioning system. Do the study and don't ask people to make those choices for you, you'll be taking the enjoyment out of it that comes with study and hard work, enjoy the process.