I use a simply multi machine setup for rendering. Its a great way to make use of old computers which still work, but are not fast enough for work.
I use backburner from autodesk as my server client. I use my main Workstation (i7 3820, 16gb ram) as the master, and then conect the other machines as servers. I can connect them all by simply connecting all the machines to one router.
You can control the machines from he mater machine, so the servers don need there own input devices and screens, which helps money wise.
You can set it so that all the machines render to a main drive, or o there internal hard drive.
If you go for 1 drive make sure its big but also fast and has a fast connection to all machines.
For the servers work out what you need to render and get nothing more.
Graphics cards are not really needed, just enough ram to process the info you give it.
In terms of rendering, I usally spilt the scene in a number of renderable chunks and have the machines work on there own set of frames. You can have it set so all the machines work together, which is very usefull if your working on a still and want to speed it up.
For adobe, you can get a background server, I forget the name, but you can buy a number of after market control programs too.
Hope that answers some of your questions, let me know if you have any more.