Custom rack, isolation under platform vs component?

And it's hard to see from the picture, but the whole rack is on bigger isolation feet, so the rack is isolated from the floor. 

Your rack looks nice. Perhaps you will make a second edition bassed upon trial and error and the rack will be ridged. Honestly, I believe you need to experiment with your new rack to see what will sound best, based on the questions you asked. From my past experience, I do know that you want a very solid frame with no shimmy or shake.

Nicely done but heavy duty is key  to keep from having any movement. I've built two and outgrew them both,  one is torn apart and I have some nice maple back on my  lumber rack and the other one I gave away.
I have some 8/4 quartersawn red oak  drying as we speak for a six tier single width rack and am working on a plan. Adjustable shelves would be nice but not sure how to implement.

Yes, thank you. I am thinking that I will bolt the platforms in to hopefully increase rigidity. I assume that would be most beneficial even if others say they prefer the feet under platform vs component. In my case the rigidity should probably be addressed first. 

Components.

Nice job on the rack.

Do you have concrete or a wood floor?