Speaker advice (floor plan attached)

I'm currently running a 3.1 system with a pair of Polk RTi8's and a CSi5. In anticipation of running a 7.2.4 system someday, I've watched for bargains on matching speakers and have in storage a pair of Polk RTi6's for the rears, a pair of FXiA6's for surrounds, and (4) RC60i ceiling speakers. I'm planning on getting a Denon x6400h and one or two Rythmik FV15HP's.

We have been planning for awhile to buy a new house, and so I went with the bipole surrounds thinking I'd be repurposing a medium size room and they would only be a few feet away. However, we have decided to build a house and we are going for an open floor plan in the basement. I've attached a floor plan of the layout we have in mind. We are not pursuing a dedicated theater or arranging the entire room around best possible sound, and we're OK with that. No sound treatment, hard floors with area rugs. Room volume is just under 9,000 CF with 8 foot ceiling.

Questions:

(1) With the distance from the listening position to the surrounds, is it possible that another pair of RTi6's would be a better choice for surrounds? Would it be significant enough difference to warrant making a switch at this point with the FXi6's already in my possession?

(2) I know the surrounds and rears should optimally be at ear level, but there are going to be things along the walls that will conflict. Would it be that detrimental for them to be up high on the wall?

(3) Since this is not a dedicated theater space, I have some reservations about locking our sofa into one spot forever with the ceiling speakers. And the sofa won't even be there when the contractor installs the speakers, we'll be guessing where to put them based on this generic plan. I'm sure it would sound better to have 4 ceiling speakers equidistant from the listening position. But let's say the sofa ends up moving forward or back, or worse, to the side to accommodate a sectional. In that case, would having the listening position off center from the 4 ceiling speakers still sound better than Atmos speakers on top of the towers?