I HIGHLY suggest you check out www.avsforum.com. You will find answers to all of your projector questions there. Having said that, CRT projectors can provide the highest quality image in a controlled light environment. CRT projector's usually come with 7, 8, or 9 inch CRT's. I would not consider a CRT projector with less than 8" tubes. They are very large and require someone with expertise to be properly set up. A 9 inch CRT projector is capable of producing jaw dropping images with resolutions up to 1080P if you have a capable video processor. Believe me, 1080P is almost like being there. CRT projectors are old technology and can be found at very reasonable prices these days. I disagree that they require a lot of maintenance. Mine was properly set up over 8 months ago and has not been touched since.
Digital projectors are small, easy to set up, do not require as much light control, and can produce a larger image due to their brightness. However, for this convenience you are giving up picture quality. No one has mentioned the DiLA digital projector which is considered by many to be better than DLP or LCD.
You can obtain an awesome projection system with a 20k budget. But please, please do your homework before you take the plunge. If you go in uninformed, it can cost you big time.