Most adjustable keyboard trays commonly found in office-type furniture will work fine with this keyboard, like this one or this one

The cheap, narrow kind of keyboard trays that you can find in the self-assembly desks (like this one) probably won't allow this keyboard to fit, but if you're concerned about RSI, chances are you don't have a cheap desk like the one in the pic.

It really depends.

At work I use a Microsoft Trackball Explorer which is probably one of the best trackball mice ever made, and are nearly impossible to find nowadays.
I know a few people that use the Logitech Cordless Trackman Optical and love it, but it didn't feel confortable enough for my own use.

At home, I use a Logitech G9 mouse and a Ideazon Fang for gaming sessions, but for everything else I tend to just rely on keyboard shortcuts to navigate around my desktop.

I've been using a Kinesis Advantage keyboard for several years now and I have to say it's probably one of the best out there, specially if you have issues with RSI.
I ended up getting two; one which I leave at home on my workstation, and one that I have at work.

Programmable, very good tactile feedback (almost as good as the Model M), can be switched to Dvorak, and their support staff is phenomenal.
It will take you maybe a week or so to get accustomed to the key positions, but once you get the hang of it, you'll never go back.

If you're in the market for a good keyboard that will last you years, definitely have a look at these. They're a little pricey (about $300 or so, depending on the model), but they'll be the best money ever spent on a keyboard.

Yes, you can.

There are 4 drive slots located below the power supply towards the rear of the case.

1) open the side panel,
2) remove the drive tray in one of the empty slots,
3) place your drive in the drive tray, slide it in,
4) connect the SATA and power cables,
5) close the side panel.

That's it.