gas
1. What is the cheapest decent model you can buy?
Like anything, it depends on what personal standards you have. I got the cheapest one I could find and was V.Happy with it. Other people might think it was crap.
2. How does the image quality compare to a standard modern CRT ?
This depends on what resolution you buy, and blub brightness. With my one, it's obviously not as bright as a CRT but my eyes can't notice a difference in image quality. The pixels are bigger. you can run it off RGB scart or composit video. This makes a difference.
3. What size room would be required ?
I have a 'normal' size room. What's more awkward is where to put the furniture. You can mount the projector on the ceiling, but will need to make room for the screen, or projection area.
4. What size can the image be without losing resolution?
My image is about 10' and I haven't lost any resolution. You'll probably run out of wall space first.
5. What make /model can you recommend ?
I got an Epson. I don't necessariliy recommend this over any others - I haven't tried any others.
6. What type of screen do you recommend ?
I first projected onto a sheet in the garden. That was great. It was like a drive in movie. At the moment, I'm using the wall in my living room. I haven't got a screen yet.