If you don't mind a ride down to Horsham, Jeff Paynter of
www.projectorsareus.co.uk has great set-up and a plethora of projectors. You'll get a good demo, and he knows his stuff - he's been in the business (including films) for a good few years, and will be able to answer any questions. He's not a clueless salesman. Not sure if he does full installs though, but I wouldn't be surprised if he did - he has loads of AV kit including sound systems on dem too. Best to contact him and find out.
Jeff Paynter is a Sim specialist and knows the models well. He has calibrated some of his pjs using measuring devices, and as I mentioned before, the HT200 DMF produced the best image that I saw on my demo. The HT1000 was very close, and at the time around £1000 cheaper. It was also quieter, and had more options/higher res, so that's why I chose it.
Quick mounting for a ceiling mount look like your best option, if the projector will have to go above your head. I made a ceiling mount from a both a plastic and metal speaker bracket which are quick release - two types here:
http://www.g-lightfoot.pwp.blueyonde...k/ht1000.html?
I'm sure you can buy them like that (the second type in particular if it has to hang lower down).
18ft of cable souldn't be a problem - I'm running 25 to 30ft of various cables to my HT1000 with no problems (7.5m DVI too).
Complete light control can be an issue - less so with a grey screen, but if you can make up some blackout cloth to cover the window gap each time you need to fully darken the room, that will increase your range of projectors (not just high brightnes models). A few squares of velcro on both window and blackout cloth will do the trick.
Convected heat may be a problem, but only insomuch as the pj may go into high speed fan mode if it warms up. Mine has done that whilst playing recently due to the heat we've been having. Projectors have built in shutdown protection should they get too hot. I notice the speed up momentarily, but forget about it as I'm watching the film. It's very rare though.
29db or less is meant to be quiet, but it depends on how close you are to it.
The new Domino is 1024 x 576 and therefore no advantage resolution wise over the HT1000, so if you want the higher res, you may need to look at the other models in the range. Should produce a fantastic image though, and seems great value at just £3750. Jeff will probably have them both on dem, so you could do a back to back viewing if you wanted. I have a feeling the Sim will be more than marginaly better than the HT1000, but the only way to tell is to see for yourself.
HTH
Gary.