I had a similar issue; lots of stuff, very limited space. First thing to do, is go through all of it, and get rid of all the crap you never going to use. I found so much junk that had been sitting there, stuff I had forgotten about, trash etc. Some of it I was even able to sell to help pay for the new shelves. After that, I mounted shelves on pretty much every wall I could. I mounted them low enough to allow to 10 gallon totes to be stacked on top of each other with a little room on top. We then purchased 10 gallon totes and put everything we could in them, labeled them with their contents and started stacking.

Shelves: https://www.lowes.com/pd/97-in-L-x-0...lving/50386830
Brackets: https://www.lowes.com/pd/Style-Selec...racket/4651455