Walls, Ceiling, and Floors
A perfect home theater has flat black walls, ceilings and floors. That said, even those that have that option, probably won't go all black. That's OK, the trick is to get the whole room as dark as possible in terms of reflective surfaces. 50 years ago, movie theaters were so dark, that in the moments nothing was on the screen, you'd be lucky to see your hands in front of your face. Today, due to fire laws, movie theaters just aren't as dark. Here in California, there are sconces on the walls, emergency lighting signs and emergency lighting on the steps, etc. I can certainly get my own theater, which doesn't have black anything, darker than anything at the local cinemaplex.
You can certainly have a good viewing experience if you have off white walls and ceilings (and whatever for a floor), but, the more you can darken all those surfaces, the more the experience improves. Consider:
Lighter surfaces reflect more light back onto the screen, even if you have zero lighting in the room. That will degrade your black levels, making the image less dynamic.
I finally made the move in my room. For the last three years, my larger theater (a "great room" with high ceilings) had off white ceiling and walls, and a medium gold carpet. Picture viewing was wonderful, but not anywhere as good as it could be. Finally, a few months ago, everything was ready, and the room was repainted a dark rust color. My wife wasn't going to tolerate black anything, as we use the room for general use, and entertaining. The dark rust is dark enough that only a tiny percentage of the light that used to reflect back, now does. It's so small, that there is no detectable color shift from the rust color.
At the same time, I had the off-white ceiling darkened about 5 shades. I'd say it now reflects no more than 20% of the light it used to, probably less.
Oh what a difference. everything that looked great, became spectacular.
So, take a look at that room. Do what you can to darken the surfaces.
Use of rich dark colored walls has become popular, at least out here in California. That's a help. Faux walls too, such as I came up with for my old room, in the image above. Hardly a fully dark surfaced room, the improvement in picture quality was quite obvious.
Two primary issues here to consider - size and type (screen surface)
Figure out where you will be sitting, how large a screen you would like and make sure that the projector can be placed in your room, to fill that screen from where it needs to be placed.
In addition if you have side lighting, or some ambient from those windows, consider what screen surface to choose.
High contrast gray screens will reject a large amount of side light. I have always had a HC gray screen, and believe me, it really helps compensate for some of those room "problems".
We have a number of articles about choosing screens, and the differences between different screen surfaces. In addition, you'll find screen recommendations in each full projector review. Some additional info will also be found in on the Screen Recommendations page in this report, but not specific recommendations for individual projectors.
How far back to sit
That's up to you. You already know where you like to sit in a movie theater. In your home, most likely you'll want the projected image to take up about as much of your view as it does in the theater. Due to reasons I won't get into, you'll probably end up with the screen in your room, taking up a little less of the view than when you are in the theater.
Keep this in mind - a big part of getting immersed into a movie, and the ability to "suspend disbelief" that we get in movie theaters is due to the huge amount of your view that the image takes up. A good chunk of the rest is due to everything else around being dark and therefore "not on your radar". You are looking to be immersed in the movie. The right screen size and seating (and other room conditions) are all part of that immersion.