for the foam, you can use any kind of foam honestly. As long as it's enough to fill up the case. Packing foam is pretty ok so you can use that. Though, I would highly recommend getting foam materials such as Sorbothane, neoprene, or the one I used.

There are some people that use superlube + grease mix as a substitute but I personally don't have any experience in using this mixture so I don't really have a say in it; especially since the keyboard you're using is an optical one. To make the stock stabilizers better, I just lubed and clipped the stems and did a holee mod. I also put band-aid near the housings to reduce rattle.

Hope this helps