An interesting but I am afraid difficult question... I had asked that question myself as well... What's a good setup? Thus:
A) to make as efficient as possible use of the available HP-rack space
B) position the modules in such way that you have them in a logical order next to each other or at least in each other’s "neighbourhood"
If you just look at point B only and don't even take the space matter into account, that's a huge puzzle... The more modules you get the bigger the puzzle get.
Roughly I start in my modular on the left-hand side with clock modules & sequencers, then oscillators and LFO's, followed by filters, envelopes & others and VCAs & mixers and to end with the audio input/output modules at the right-hand side because for me at the right-hand side my external mixer stands next to my Eurorack ;-)
But as you mentioned already by yourself, it's a rather personal thing. You should do what works for you in the most pleasant & comfortable way. Or if you really want to improve your module-positioning: try to monitor yourself for a couple of days or weeks how you patch which modules with which ones and then see if you have a lot of (unnecessarily) long patch cables, those might be an indication that you could put a few modules closer to each other. I think the larger the setup becomes you can't completely avoid long patch cables though.
So I was struggling with that as well but I kept it roughly as above described and solved my space issue by just buying another Eurorack case. Why bothering yourself with such a difficult puzzle that every time becomes more complicated when new modules are added if you simply can solve it by getting yourself another rack to solve the HP-rack space issue? ;-) Might not always be possible, I know. I only can do that one more time and then I don't have space at all any more for the Eurorack stuff to extend but at the moment that was the nicest solution. Now I am happily adding modules without the concern of HP space (of course till a certain extend) and as long as there are not too many long patch cables, I am happy with that solution and don't stress myself too much with how to make it more efficient --> because it’s an almost impossible puzzle to solve. I think we all can use that time better to put that time into creating sounds ;-)
Not sure if this helps you but what I am trying to say is... don't stress yourself too much about this... if possible get yourself just more HP-rack space.
Also don't migrate to too many small modules because then sooner or later it's getting too congested and the patch cables are blocking too much your modules and knobs might be difficult to reach to use them comfortably.
Kind regards, Garfield Modular.