Starting with the basics there are tons of sites with writeups on things including here, as well as
www.projectorcentral.com and
www.projectorreviews.com I would start with doing some homework there. The projector itself is an excellent choice and is easily one of the best models under $3K on the market right now.
The ceiling fan jumps out as me as the most obvious issue. Basically, if you can't draw a straight line from the top of the lens, to the top of the screen because anything is in the way, then you have to move that 'anything' to get a clear line of sight.
Sounds like you addressed that already as something you are aware of.
The 6500 has a lot of lens shift, something which some projectors don't have. So, Isiberian, who has to use books to bring his image down, is not something you will have to deal with. Instead, you will get optical lens shift which will allow you to place the projector a foot or more above the projected image (read reviews for specifics).
At 12' viewing, with that quality projector, you really should be shooting for about a 110" diagonal or so as a minimum. This would put you in the right range for THX specifications and a 'center of the theater' feel to your projection. The obvious issue is that you are going to have to watch the overall width of the screen including the border & bar at the bottom to ensure they don't interfere with your speakers.
Now, if you have the speakers out from the wall a bit and can squeak the screen in so that it falls between a flat panel display and your speakers, then that can give you a few extra inches which may be excellent for your setup.
My typical statements...
If you are going to be using a retractable screen then go with a cheap manual screen or go with a tab-tensioned motorized screen. Non-tab-tensioned screens WILL develop waves in the materials after a year or two of use due to environmental reasons (not because you roll it up). So, you don't want to spend extra $$$ on a motorized screen and then have it be just as bad looking as a cheap manual screen a couple of years down the road. That's basically throwing money away.
You can go cheap, then look for deals online, which can give you some good value if you are tight on cash to start off with, or you can go to the usual manufacturers including Da-Lite, Draper, or Stewart.
This is an excellent screen, but shows that you have limited choices for a fair amount of savings when you go to eBay...
http://cgi.ebay.com/DA-LITE-88524-106-Tab-Tension-Motorized-Film-Screen_W0QQitemZ180354809040QQihZ008QQcategoryZ48655QQssPageNameZWDVWQQrdZ1QQcmdZViewItem
106" - but a flat white screen, yet the built in low-voltage controls are a nice addition, and the eBay price is less than cost - which makes the price very good.
In your room, if you are going to stick with what I imagine is light colored walls, white ceiling, and medium carpeting, you will get some (small) benefit from a grey screen. Something like the HC Cinema Vision from Da-Lite or similar from other manufacturers is good.
Plan to spend about $2K or so on the screen if you don't find something you are really happy with on eBay. Yet, if $2K is to much, then I would strongly consider what I linked to above. Bottom line is that 106" sized tab-tensioned screens don't show up that often (I look) from quality manufacturers. I personally lucked into one a few years back and it has been great.
You will want to plan for mounting the screen appropriately which means with a kick-off from your wall to allow for it to come in front of your display. This may also mean building a soffit around the screen to hide it from view. Keep in mind that screens are rarely pretty to look at.
I'm not 100% sure where ventilation is with the 6500, but you want to be sure to be far enough away from walls and obstructions, per the manual specifications, to allow for proper ventilation of the projector.
Finally - don't forget that this stuff all needs power to work, and I didn't see an outlet up on that wall. You will need to deal with that appropriately.
Finally (again) - consider the room lighting with spotlight type lamps to allow for reading while the projector is on.
Check:
http://www.avintegrated.com/lighting.html for an idea of how directional lighting can really allow for multi-purpose use of the room while still enjoying your projector.
