Reasonably how long would it take to complete this game's story?

[Del Murder]

Miriel ran the game on Bootcamp Windows for years and had no issues. It's not hard to set up a Windows partition on Mac.

[Citizen Bleys]

I heard some shenanigans about needing a "gaming controller" for my computer to enjoy the game better.

Yes, just like every other FF game; they're meant to be played with a gamepad.

EDIT: Also does anyone know if this game is available on a Mac? I see nothing on their site

You could use BootCamp, Crossover Gaming, or WINE, but with anything but an actual Windows install, you wouldn't be able to use Windower, which adds a lot of functionality that should be part of the game. I can't imagine being without the rangefinder, it helps me know when I'm far enough away from an aggressive mob to avoid aggro (15 yalms for sound, 25 for sight), and Infobar, though not always accurate with newer mobs, is an easy to tell which mobs are aggressive and which ones aren't.