Dread

I am new to the forum, and if you wouldn't mind entertaining a question from a newbie that would be great. I am am going to install a 7.2.4 system in my dedicated HT I am building. The room dimensions are 14'x20'. I plan on an Atmos setup and I have read that you don't want bi-polar speakers for surrounds. My original system consisted of 2x RP-280, RP-450C, 4x RP-250S, with 4 in ceiling speakers. Does this look like it would work? I have another question, it concerns mixing in wall surround with tower front and centers. Would the imaging and voices of the speakers work together in this scenario? For example if I used RP-280s and RP-450C up front, could I install say Pro-6502L-THX for surrounds? Would they sound appropriate together? I see a new line of in-wall speakers are out the Klipsch PRO-180RPW, could I use this in place of the THX speakers? Sorry for the load of questions, I am excited about my theater project.