Caravetta

It looks really nice. I like how it scrolls down but mybe you could put in a way that when you are at the bottom it will scroll to the top when it is clicked.

1. Essentially a home server is to store files, redundancy for those files, and easy access to them from within the network, and any service you want to run (web server, game server, teamspeak etc...) Its like a NAS, but its a normal computer.
2. WHS (Windows home server) is the most popular distro for this kind of server, it integrates well with other windows machines on the network. As for the hardware, a plain storage server can be run on a Core i3 or older Core 2 Quad/Duo, but since you will be rendering you will need some horsepower like an i5, i7 and if it supports Cuda or OpenCl a graphics card would go a long way (preferably a Quadro since you have something to do with AutoCAD).
3. A hardware raid controller is a pci-e addon card that lets you connect a lot of drives together then run them in a raid (redundant array of independent disks) array to provide speed, redundancy incase of a drive failure. For running a 24 drive array you will need a quite high end controller something among the lines of http://www.lsi.com/products/storagecomponents/Pages/MegaRAIDSAS9280-24i4e.aspx (yes they are NOT cheap), there are software options if you are not willing to invest in a raid card.
4. If you want high speed transfers and the ability to work while the files are on the server a 10 gbit NIC would be a good idea, http://www.emulex.com/products/10gbe-network-adapters-nic/emulex-branded/oce11101-nx/overview.html there are cheaper options, but still quite expensive, otherwise get a 1gig Intel NIC if the board does not feature an integrated Intel NIC.
5. If you will be using Windows the setup is straight forward, the LSI raid software is also easy to use.
6. Get a 4U or more rack mount case that has 24 drive support, Norco among other manufacturers make these.
 
Hope this helps.

I can't recommend a parallel configuration in many situations these days with head pressure being so much more important than max rate but yeah if you want redundancy then dual d5s is a great way to go

If you have the case already, get a ruler and measure from the top of the case to the top of the vrm/ram, if that is smaller than the size of the fan and radiator combined you're fine.

I just use linux and emacs it is all I need :) . I am not a big fan of IDEs I feel like they get in the way sometimes.

I think it would be a really good idea. One thing that might be cool would mybe have small competitions for example people make a game in a small amount of time or other small programs.

I agree with Ghost as well. I like to make sure that my cooling is a little more then I need so that I don't have to worry and it gives me a little room to play with.