Where to start with room acoustics

Although it's always good to be pro-active, it's possible that you just may be a bit overly concerned with your room at this point. Unless of course it's filled with windows.

Your room demensions should work quite well assuming you place your speakers along one of the short walls.

Unless you're chompin' at the bit to resolve all potential problems beforehand, I would recommend installing your system, dedicated lines, and thick berber carpeting/pad, and then analyze any possible acoustic shortcomings thereafter.

-IMO

You could purchase the Rives Audio test CD and a Radioshack sound pressure meter. The test cd allows you to measure the in room frequency response and will likely confirm what your ears are telling you. From there you can explore solutions.

Have you done a resonant modes analysis of your room, as must be done by Everest in the book you mention? (He does several in Sound Studio Construction on a Budget.) It shouldn't be over your head--just a bunch of divisions to get the modes for each dimension, then listing them in order of size, then looking at how they're spaced. If your 27' were 26', you'd be in some trouble and would need some kind of absorption at certain frequencies. You may anyway, but only a room analysis will tell. Speaker placement is important too, but that can be done by trial and error.

All this applies, roughly, to frequencies 300Hz and below. For above, absorption and/or diffusion will be called for, ideally. Everest should be clear on that. If by any chance you're handy with tools and have a workshop of any kind, I have DIY plans for one- and two-dimensional diffusors of the RPG kind, and for Argent Room Lens clones, which I'd be glad to email to you.

It's not rocket science, as they say, and I'd urge you not to give up too easily if Everest seems confusing at first. Good luck with the project!