Change of Plans

Hi all, I recently started a thread about my new project, which was a multi room studio, based on a 20' x 20' x 9' design. Here's the thread: http://www.johnlsayers.com/phpBB2/viewt ... highlight= I have changed the size to 20' x 25' x 9', and my new plan is for a single room design. I get confused by all the room mode calculators, and I was wondering if someone could answer a couple questions. (2) of the dimensions are fixed as this is an addition to my house 20'w x9'h. The lenght is not fixed at this point. Could someone suggest a room length to minimize room modes? 25' is the maximum length I can afford at this time. Also given the suggested size, could someone recommend a speaker/listening position layout , as well as room treatments. Thanks, James