Without actually being in the room I think I'd prefer to have the front speakers wall mounted, in your situation. I think they could look quite neat.
The FX speakers, IMO, are miles better on the side walls than the rear walls for a 5.1 setup. I have tried both and sides where night and day difference - dolby 5.1 setup and mixes are side / slightly behind your seating position.
When I tried them on the rear walls it just felt like everything was behind me, which sounded very odd when the mix is supposed to be side on...
If you could stack some books / side tables up and leave them on the side / rear for a while and do some testing, that'll be even better. They will sit flat and stable if left on a stack of books pushed against the wall.
You may find them being slightly above ear high probably sounds better / more spacious, however, if you plan on adding Atmos (ceiling) speakers later, then it is recommended to drop the speakers down to ear level. I found I have much better separation between side speakers and top speakers when I dropped them down to ear height.
EDIT: To say that when I had 5.1 in an old house, with fx speakers side on and slightly above ear level, that surround sound movies sounded fantastic. With my new house, I cant get fx on side walls, so used floor standing speakers side on. I never got the same effect as when I used the FX speakers. What I have done now is, used FX on the rear wall, and floor standing speakers to my sides, in a 7.1 setup. This to me sounds great now. Unfortunately its all a compromise!