Wood (pardon the pun) have thought that MDF or anything else with a random "grain" wood (oops) be better than that stuff trees are made of. Even plywood wood (whoops) be better than solid wood, at least from a tonal perspective (Steinway pianos are made from plywood you know). As long as it won't vibrate or transmit vibrations it's good. Glass, I wood think (oops again) wood (darn it!) not be good.
A lot of the mid-price hifi racks (and even speaker cabinets) are made from MDF or ply, all be it veneered, covered with some form of industrial sticky-backed-plastic as they used to (still do?) call it on Blue Peter, or such like.
If it were me, I wood (okay, I'll stop now) have shelves upon shelves, i.e. a basic open sided or at least open backed cabinet with shelves forming a fairly sturdy rigid structure, then have individual shelves sitting on halved squash balls, purchased sorbothane feet or spikes, sitting on the main shelves, on top of which I would place my hifi boxes.
I would put any turntable on a much heavier plinth, e.g. a piece of marble or slate procured from your local stonemason / gravestone supplier / kitchen worktop place and mount that on spikes or halved squash balls or whatever on top of the top shelf of the rack.
And I would sit the whole shebang on rubber feet or carpet spikes or carpet spikes with 10p pieces under them, depending in the floor.
I would not fix the thing to the wall unless it was eight feet tall and liable to fall over and crush someone.
Not withstanding that I have all the cabinet making skills of a sledgehammer, if you're up for it, and / or up to it, have a go!