Actually the Gustaburg reigon was decimated in a war against invading Sandorian troups before the Crystal Era. The Bastokan forces used firearms to beat the Sandorian Knights back pass La Thine.

Buburimu = Valkurm in many respects. Take a party and fight there, its better than Valkurm ever will be. Mandragoras(pansies), Birds, Rarabs, and Dhamels are significantly weaker than Valkurm's Lizards, Flies, and other stuff there with much less competition. I say if you can make a party there, go to it.

A WAR before 30 and even beyond that will work primarily best with a MNK sub especially if its your first time through the game. Sandy would be a good choice as well being a PLD/WAR.