Well the aim is something a bit more than a shed eventually, but I take your point. Mainly I just don't want to have to redo it. But I'd also like it to not look shit in a years time.
12mm ply over 400mm centers... which will support 20kg between each bracket
Why would you not just have more anyway?
I have 12mm ply over 400mm centers in my shed, which will support 20kg between each bracket with no problems.
Also, it's a shed. Who cares if it deflects a more.