Help FFXIII: Side quests?

[katisupahfly]

I have the strategy guide for FFXIII, and it says that I should wait to do my side quests until the end of the game, except for the Vile Peaks minigame..
I'm in Chapter 11, and I don't think I did that side quest, is there anyway I could back track to the Vile Peaks through the Gran Pulse area or no?

And, even though it says that I should wait until the end of the game, should I get at least SOME side quests done now? If so, which?

 

[FinalHeart]

The only missions I did before the endgame were the first five, or the only D level ones. It's a lot easier to go back later because then the C level missions will be extraordinarily easy, as well as most of the B level ones.

 

[finalblackmage]

Ya, I was able to do all the missions that come before the storyline ones easily, and tried at a few of the tougher ones with no luck, so I just went forward.