Unlike the other chapters, Chapter 11 consists of many locations to explore, and Vallis Media is the first. Also unlike other chapters, you're not really expected to do everything in Chapter 11 before finishing the chapter—you'll be able to come back here at the end of the game. It's questionable whether some of sidequests here are even possible without unlocking Crystarium stage 10.
My notes on this chapter basically assume that you will complete the first 28 missions on your way through the chapter. Most of these are optional and can be easily completed later, but it is reasonable to do them the first time through, and doing so will unlock some useful travel options that will help in the long run. It is entirely possible to do missions after 28 as well, especially if you beat the Chapter 11 boss (and unlock Crystarium stage 9) but return to the previous parts of the chapter instead of moving on to Chapter 12. If you decide to do this, you may have to ignore references to abilities or items you don't actually have yet in my notes.