Microsoft and Sony have different standards for how things work. It's typically the case that I believe 360 games will pause with the guideblade is pulled up, but it is typically the case that PS3 games will not pause with the XMB pulled up. Whether or not the game actually pauses because of that I don't know. I tend to do that sometimes as well thinking it'll pause, but often the game continues to run it just won't proceed to a new action.

Beating the game though is less about having so much completed in your crystarium and more about having the right strategy. So you can beat the game with a lot less than seems required. And since you don't get exp for kills in the first chapter or two until you get marked. There's not really a lot of a point to fighting everything you find unless you want the items. Which upgrading is not really a huge deal since you can get by with other things and very modest upgrading.