Re: case design, one aspect I'm really enjoying in eurorack that I think might be a little odd or unique is designing each case on its own terms as an instrument with particular goals in mind and limited range, that limitation helping me to be creative and learn. I've got an acid rack now, a drone rack, and a modulation focused weird ambient rack (R.I.P. my wallet). To do this you end up duplicating some functionality but that's also an excuse to try out new modules, and in particular to take modules that are underused in one case and to move them to another where they can shine or contribute in new ways. It also results in a lot of moving pains but I kind of just accept it because it feels worth the hassle.
I'll also note I've naturally gravitated towards the flow approach @Lugia laid out, but like you @farkas I'll put modules in odd spots if it makes patching easier or I want direct access to one, and yes sometimes if I'm just feeling lazy.
Good topic to bring up and I'm curious what others are doing.
my tunes: https://stevehand.bandcamp.com/