I've added dimensions to the front page of the Chalktendo. Check back there to see the dimensions. If you have additional questions about them, you can email me through the website or keep posting on this threat (or PM me here).
As for my USB and controller setup...
I believe we have the exact same USB converters. My N64 ones are also the clear-blue ones that you can get on EBay every once in a while. I have 4 of em, but I've only tried using 3 at ones so far, and they work fine. They have a switch for switching between PS2 and N64 controllers with a green and red LED on them. The SNES adapter I have is also the Super Smatjoy. I use it and the SNES controller for SNES, NES, Gameboy, and Sega Genesis/Master System games (I know, sacrilege). Of course, sometimes I use the arcade controls for these as well... depends on how I'm feeling.
The Super Smartjoy works great, but the key to the N64 controllers are finding quality N64 controllers. If they are too sloppy they don't work well. Both adapters plug in easy and are immediately recognized by Windows XP. I then just set them up in my emulators and away I go. Because of the dual-control nature of many of the games I play, I have 2 emulator configs for many console systems... one with the arcade controls and one with the joystick/controllers. I run one emulator or the other based on what control type I want to use.
Finally, I hook them up to a powered USB hub in the front of the unit that actually plugs into another USB hub inside the control panel. This way, I have 2 USB hubs in the front unit, but only have to run 1 USB cable back to my PC in the back unit. This has worked for controllers really well, however either the daisy chaining or the hubs themselves do not prove conducive for USB hard drives, etc. to backup. I plug my USB hard drive into the PC itself via the front USB ports at the front of the PC (accessable at the side of my unit) for backups.
Hope this helps!
--Jason