Jaspers 4D-120B shelves

Hi, I just ordered a keyboard stand (4D-120B) from Thomann. I was planing to make shelves for it to have a bit more freedom when positioning my gear on it.

Do you have some recommendations for the measurements for the shelves. Probably the width should be around 120cm but what about the depth?

The lower section has supports that are 60cm long and upper sections supports that are 40cm.
Should I make the shelves with similar depth or can they be even deeper?
Will a 120cm wide shelve fit?

If any of you have experience I would highly appreciate some advice!

Just be careful what material you use! I used some ikea plywood shelving and my V-Synth dropped onto my Pro-2 (no damage thankfully). Of course this was entirely my fault as I only used 2 arms to support way too much weight. I ended up ditching the shelves and forking out for more arms!