If your'e going to dedicate one room for home theater, first thing is making sure you have all the wiring ready prior to doing the installation. That means making sure you have all the speaker wires run for a proper surround sound effect. That also takes into account the powered subwoofer. Next, if you are going with a front projector, make sure you have proper video cables run from the projector to where you are going to have all your equipment. A personal suggestion is to run 2 HDMI cables, a composite video and a CAT5E cable from where the projector will be to where the rest of the equipment will be. DO NOT run speaker wires to the projector. Many people make that fatal mistake. DO NOT run speaker wires to any tv location period. Video cables yes, speaker wires no.
Make sure you have power for the projector too in the ceiling. If you're going to have a electric screen, it will need power too.
The lumens rating is based on what kind of environment you plan to view movies or tv with. If the room is going to be a dual purpose room like say a family room and a home theater room and you want a front projector, then you would want a higher lumen projector so that way you can still see the picture in a room full of light. If you are going to have a dedicated room with seating, dark paint, and all that, you need a projector with a lower lumen rating. This will give an awesome picture quality in a dark to dim lite room but the cost factor goes up higher. Usually your cheaper priced projectors will be the ones used for power point presentations or other fixed image use and will have a high lumen rating. They however look fair to poor in a dedicated theater application.
Screen application is simple. If a dedicated room, go with a fixed position screen. It is cheaper and does the job perfectly. If the room is dual purpose, then a motorized screen is in order. More money, requires connections to lower and raise, and you will probably need another tv in that room for watching the news or weather since its kinda over kill to watch that stuff on a projector.
If all else, consult a professional who has had experience with dedicated home theather systems. Usually they can make the best recommendations for what you want to do. It will not be cheap, but in the long run, it will get done faster, cleaner, and work longer too.
I have designed many a home theater system for people over the last 6 years and can tell you that if you go full dedicated home theater, you will have no regrets. You will be the envy of friends and family for years to come.
Good luck.