Getting whatever job is your favorite to 50 as your first is viable, don't let others tell you otherwise.

Playing a tank job on PS3 is no issue, at least it hasn't been an issue at all for me when I leveled PLD. So if tanking is what you want to do, definitely go for it. You don't need to learn the duties beforehand (it does help for sure, but part of the fun is learning them for the first time as the job you like most).

The only issues you might run into are people who leave before even trying because the tank isn't "geared enough" (sometimes legitimate, but generally not from my experience). Or if you run into players who flame you for a single mistake (tanks in general take the brunt of the abuse from other players for mistakes, their mistakes are more noticeable and people see them as easy targets).

I say if you want PLD to be your first 50, go for it.