By the way, I'm about to order a Z2, so I'm not an expert by any means, just someone who's read around a lot now. We're going for a 92" or 96" diagonal screen at a distance of 3.1m, but the room itself is 5x3.3m. We're actually going to order the Z2 first, then decide what exact image size and position we like before committing another 600 quid.
The things I *can* comment on are PJ heat, and your speaker options.
We use a projector at work in our conference room, and the effect really is like a fan heater - far worse than a PC exhaust.
(incidentally, even though it has a lousy 300:1 contrast, movies look pretty cool on it at lunchtimes

)
As I mentioned earlier, my study is only a little bit smaller than your room. I've got one of those fancy new creative 7700 7.1 speaker sets (only £80) attached to the PC, and the results are pretty jaw-dropping in this size of room. I love our big Mission 77s down in the lounge, but they'd be a audio insanity up here!
If you're planning a playroom, I'd not be afraid recommend some small satellites that you can mount up out of harms way.