I replied earlier to a post regarding a scanner recommendation, concurring with the consensus Fujitsu. At the end of the post I stated I do not use IT products intended for home use in a commercial environment, which 9 clients certainly makes; that's again my point here.
I have two Dell servers, one running Unix 24x7 for probably a decade now without a single hiccough and a two year old single-raided T 310 created specifically for AC which has also run flawlessly. I bet I could have saved money on the AC server going with off-the-shelf desktop, recommendation in early 2010 when I first downloaded AC, but at what cost had something not intended for heavy use collapsed?
With regards to the OS, you're not going to get better advice than from fellow forum contributors Wendell and Bert customized for AC, although if you're curious, the Ac Server with an equal number of clients as you is running 2008R2 SP1 with all the necessary CALS and SQL server 2008R2 standard.
How ever you decide to proceed, best wishes.
GNicoll
