> More lumens is better - as this allows for watching in rooms that are still reasonably well lit
Forget "reasonably well lit". In my experience, if you have as much as a table lamp turned on, you'll get a washed out picture. To compensate, you'll have to have the projector lamp always running at full intensity, which will only decrease its lifespan (which is already shorter than a TV). It'll start getting progressively dimmer long before what it's rated for.
> Short throw/adjustable throw - the projector will be sitting about 3m away from my wall.
I don't see the "epic gaming/movie area" you're envisioning if the projector's going to be this close to the screen. I get the impression it'll give you a picture so small (relatively speaking) you won't get the benefit of having a projector in the first place. There are calculators out there that'll give you the min/max possible sizes for a given distance--I suggest you look into those to see what's even possible.
> 1080p equals a big price jump
Maybe so, but you won't get the "epic" setup you're after with a projector that can't do that. Are you ok with non-HD content blown up over a large area? A lot of people, now used to HD, complain how poor SD is, especially over a large area. It doesn't bother me personally (my projector can only do 1280x1024, with the picture roughly 7 feet across), but it might bother you. Keep in mind also that a lot of older lower-resolution projectors have a 4:3 aspect ratio, so if you want to watch 16:9 content on that, you'll be left with a pretty small picture, vertically.
Keep in mind also that projector lamps are only good for 2-3000 hours, and you get what you pay for. Some are as expensive as what you're planning on spending on the projector itself.
Bottom line--I'm not trying to rain on your parade, but I don't want you to set yourself up for disappointment. I'm a big proponent of using a projector instead of a TV, and I've been using nothing but projectors for a dozen years or so. I'm currently on my second one, and both are pretty low-spec--so I know what to expect at the lower end. It's great to have a big picture on the cheap, but I don't go thinking it's any better than a TV of the same screen size. I'm definitely making the jump to 1080p for my next one, if 4K isn't already mainstream (and prices have dropped) by then.