Should I go for the math behind it or are there any "general rules" that apply on pedals that I should search for?

Of course there are such rules but any "general rule" has simplified/verified/establised AFTER math calculation apply..

Things aren't so complicated but, at least, you must use some elementary math implemetations..

(Ohm & Kirchhoff laws need nothing more than sum/subtraction/multiplication/division..)

If you prefer general rules, you can search for something "transistor calculations using rules of thumb"-alike..

(as far as you're sure about your memory strong state..)