I'm at stage 2, plus a stack of bricks and pieces that don't appear to be associated with one set.

The key is to not have a house big enough to house all the Legos you want, that way you can't buy them so you never need a sorting system other than "keep the sets together". At least that's what has worked for me.

As a building toy, using the properties of how we build, i.e. stud counts on top and bottom, made sense to me

https://marquisdegeek.com/lego_organisation