I'm using a Epson 6010, (basically the same as a 5010). I sometimes run a 60w light that's app 15' from my pj screen, which is 126" 1.3 gain. True it will wash out the blacks a bit, but even in ECO mode, it's still a great picture with some ambient light in the room, (I have white walls). This pj is very bright and can handle some ambient light pretty well, so np during the super bowl parties where you need some light while entertaining. Link to some insights to screens and this pj with some ambient shots.
I'd expect to spend a few hundred on a good screen. Paid $900 for my fixed several years ago. A Vutec brite white. You can spend several thousands on 'em, but I don't think you'll need to spend more than a few hundred these days for a decent screen.
Another thing to consider, most pj's aren't meant to be operated like a family room tv might. Turning them on and off repeatedly puts more wear on the bulbs resulting in less lamp life. Something to consider if you have the kiddies operating the tv.
Mounts can be had for little over $100, or make your own. The 6010 actually comes with a mount, extra bulb, and 2 pair of glasses. I seen where someone used a satellite dish arm
Turned out pretty well actually. Some cables from monoprice, redmere the best, but costs a little more, or some 22 awg if you going over 15' in length. Consider 3d glasses if you want to try that out. Bestbuy has had the playstation glasses on sale sometimes for around $40 or less. Work fine with the Epson. Pretty good deal. Otherwise looking at around $90 for glasses from Epson.
The Benq is a nice pj, but I think if ambient light is a consideration, the Epson might be a little better in that regard.