All jobs are useful but they're not all necessary. You can complete the game and only master a handful of the best ones. I mastered pretty much all of them but you don't need all of them to win.

Getting the Triple AP egg is a requirement if you want to master everything. It'd just take too long without it.

You'll probably have more fun if you don't shoot for 100% in your first game. There's too much pressure to do everything flawlessly.