Definitely good advice - decide on the type of space that you're trying to create and then you can get more focused help on the specific elements of the design, construction, equipment, installation, etc.
As an aside - some of the more popular "completed theater" threads have enormous post counts and/or appear to be hugely complicated, but don't get psyched out by it! Scan through to find images of the finished room and decide on what you like. Even the most complex theaters can be broken down into bite-sized pieces (although the "cost per mouthful" varies hugely!).
One of the great things about this hobby is that you can define your own level of involvement - some folks just enjoy the experience of watching a movie, so are willing to write a check for someone else to do all the work (or settle for a more "out of the box" approach), and others like to noodle over the selection of each individual component, with the journey being just as rewarding and enjoyable as the actual arrival, sometimes more so.
Come on in, the water's great!