How much Bandwidth does FFXIV use?

[Impulse]

Really, your main concern bandwidth-wise will be the initial download/install, major patches and the possibility of needing to re-install for whatever reason.

[Taliesin]

I live rural too, and my only options were either satellite providers or a poor 512K.
Satellite ISPs will allow you a higher speed, but a latency averaging 700-1000ms.
I played like this for 2 years, but it's clearly not the best thing to do (Ifrit extreme was impossible for me).

I tried the 512K, and honnestly, I have ZERO problem.
The game runs smoothly, no lag or latency detected. The only problem being the time needed for big patches, but well... let the download run a full night and play the day after, not that much of a deal...
I know some LS partners use the 3G/4G technology as well, so you shouldn't have any trouble.