1. Access! Access! Access! Technology changes. You'll need to run another wire or two or three... I guarantee it! This time, the bottoms of my soffits will be removable so I can run new cables when technology changes or I just need another wire for something.
2. Flexibility/modularity: When your design gets stale or it's too bland, or you want to correct your mistakes (i.e. You read these forums after building your first theater, me
), it will be a lot less trouble to get rid of the old and bring in the new.
3. Flexibility/modularity part II: Carpet first then install columns. My first theater had columns framed first and then I drywalled and then came the carpet. Now that I'm renovating my theater, I have had to do some nasty drywall removal and the carpet has rectangles missing where the old columns were. I hope to patch the carpet, I have extra, but it has a fancy pattern so it will be tricky. This time, columns are being designed so that they are independent of the walls. Carpet will go in before the columns, then I'll fasten the columns to the walls. Also, the side panels of stage will be removable in case I want or need to redesign them. If I ever remodel again, it will be a lot less mess and trouble.
4. Get the biggest screen you can afford/fit. If your picture is too dim then mask it down. It's awfully hard to stretch a screen.
When that new brighter PJ comes on the market you won't have to buy a new, bigger screen.
5. Read these forums!