the case walls should be cheap and easy to modify and replace mdf is a good easy material to use easy to get and strong for most uses and light, 3/4" to 1" are needed to deal with the weight. the mobo stand offs are cheap and velcro straps and zip ties to hold heavy things in palce server heat sinks will hold in palce but to be sure mdf is easy to tap screws into. this case is going to made from scratch because server mounting hardware is hard for most pc case see linus's video on that part due to weird mounting. hdd's you can velcro down with and the fans mounting is easy have a tiny fan controller that has the fron case fans pulling alot more air and the rear pushing out air at slower speeds causing a slight positive air pressure keeping most dust out and using mdf for a gpu mount sothe gpu is farther away from the hot server parts with this you need to sheilding on a pcie cable extender double sided tape to insulate the cable with tin( or lead {lead foil does better for this but is scary to use}) foil the fan mounting holes for 120mm are 115mm stanard for mounting holes so thats easy i've made mini-itx cases before so i have some knowlegde on the mounting points. the design i have in the docs link is a napkin drawing so dont take that as the endall be all on that but the case should be able to be upgradable for later better or ther hardware.
sorry on grammer and my brian was everywhere on that
Console: Wii U, PS4, n64
PC build specs: i7-5820k@4.56Ghz. aSrock-x99m killer. 32gb ddr4 gskill 3200Mhz. R9-295x2. samsung 850 pro m.2 ssd 250gb. hgst 4tbx2 raid. silicone power s70 ssd 256gbx5 raid. nzxt red nocutis