Nah, be it steel or aluminum...it's just metal. The things to insure you get right are that every panel is touching at some point to get the grounding issue out of the way. It has nothing to do with the actual operation, but rather safety of the electrical parts from ESD.
You may also want to steal some parts or ideas from an exsisting case to insure you get it right. Stealing the motherboard tray and the back panel where the PCI/AGP cards exit will save you a LOT of time and material as no matter what, you'll just about have to end up with the exact same design anyway due to electro-mechanical standards. There's just no other way around this fact: a PCI card exits at this very spot no matter what brand or when it was made, and an AGP card exits here...and so forth. If you only want a couple of the slots, then just take those and graph them into your own work or whatever...
The next time you work with stainless use slow cutter speeds and high feed rates. It's kind of like lead in the way it clogs up tools so you can't run the cutter too fast. Also if it turns red from heat forget it you just hardened it so your cutters will just burn up trying to cut it.
Have you selected your choice of media to work with? I've found Aluminum to be very fun to work with, but it's a bit tough if you don't have the right tools. Aluminum clogs my dremel bits and sandpaper, so I have to go out and buy aluminum stuff prior to digging into alloys. But you can do just about anything to it, and do it fairly easily. It cuts like butter, it sands smooth, and can be polished to a mirror finish. Besides that, it's light. It's not as maliable as standard sheetmetal (It breaks sometimes rather than bends), but some designs are totally doable.
Stainless is a PITA. Period. It's hard, tough, and heavy. I started making a reservoir out of SS, and by the time I was almost done, I had exhausted my patience enough to just throw it into the corner and drop the idea of ever working with it again.
Use slow speeds and high feeds for cutters when working stainless.