I am about to invest in shelves for mostly old and some new-ish gear.
I have a 6 x 3 feet table and want shelves over that.
Some of my big old gear, demands 12 inch + 4 inch space behind, so a total of 16 inch deep and is 19 inch wide.
I have a stone wall to mount the system on, but floor standing is also possible.
The max weight is hard to answer, you know that gear has a tendency to just appear without you knowing where it came from;-)