bot farm help

Looking to build either;
Server rack

Or

2-4 full tower computers that could potentially run 40 bots at a time running nature runes in oldschool. Ideally i would like to break this up between a few pc's (running 10-15 bots on each machine) i would be needing to focus more on having large amounts of RAM and would a solid state hard drive be more ideal or does that not play a role for over all performance? I understand that these machines will be doing alot in the 10-12 hrs a day they will be running so i need you to help keep that in mind if you post a build for me. I understand it would be a fulltime job maintaining this size of a bot farm but it should totally be manageable between two people. Any advice helps.

-poof