1. Once you get to arround 30K Hits unbuffed you can safely gem for whatever you feel you need more (threat/avoidance). I also have different sets of gear for whatever the situation calls for.
2. For Glyphs I use SS, BS, Ghoul/IT depending on if I spec for my ghoul or not. I dont and never will (unless there is a specific boss fight that requires) glyph my taunt or IBF. We have 2 taunts if the first one fails, and I run with a prot pally, so RP is never ever an issue (more of an issue of using it all).
As far as rotations go, if you can manage it, PS then IT as IT will hit harder with BP up. But there are times when you need to get threat on a pull, so its not always good to wait.
I cast the spells that make the people fall over.