RDP... lord. Why do you want an entire GUI to mine? You are using command line utilities to mine with text miners from a GUI. That just makes no sense. Why not bypass the GUI all together.
As for dummy plugs, you have that backwards. Windows requires dummy plugs, Linux does not. Linux allows 8 GPUs, Windows does not (unless that's been fixed in the past few months). Windows is an inferior mining platform under any circumstance; there is literally nothing compelling about using Windows as a mining platform.
Refurbished $20 drives fail fairly often... the USB stick, not so much. Generates less heat and takes up almost no power as well.
I run most my systems with 3x 5970's and never used dummy plugs. Not sure what people were doing to require them. I'm not using the new catalyst or anything. You can go 4x 5970's with extenders and what not. The GUI does not slow down mining. I originally was going to try ubuntu, but there was no driver support for my usb adapters. The only real benefit to linux that anyone has mentioned here is the size of the OS. A full install of windows takes a 16gb usb. I plan on needing hard drives to sell my cases and mobo's anyway though. I actually started using 60gb agility ssd's. There just sexy... If I had previous experience with linux like I bet you have, I may have gone that route.
Heh, I assure you that the GUI is slowing down your mining. It's not a lot, but it's there. For example, I get about 396 MH/s per GPU on a set of GPUs I have under Widows and if I run the same GPUs under Linux, both with poclbm, the hashrate is around 404 MH/s. All thanks to loading up that heavyweight GUI for absolutely no reason. Translates to about 60 MH/s loss across all GPUs.
As for sexy SSDs... I'm more concerned with efficiency and profit, not how good my rig looks. My rigs live in the basement and in the data center, and unless something is wrong, I never see them. I'll take an ugly 3 GH/s rig over a pretty 2 GH/s rig any day.