1) I like the uptime on BRD. A lot of people will say that BRD is the most mobile class, and in some sense that's true. We can keep firing away at the enemy with very little regard to how we have to dodge. That said, I played MNK up through the relic quest, and I have to say, it feels way more mobile due to the fact that you actually *have to* move between attacks.
2) The game assumes that you're leveling multiple classes, anyway, so there's no real harm in changing classes at this point.
3) MNK has the higher dps ceiling, but also requires a ramp up. BRD can spike really high with cooldowns, and has very little ramping.
4) I think this would go to BRD. Most end game groups will have one, while the melee slot seems to be a tossup between MNK/DRG.