You choose how many and which creatures to tap while Minas Tirith Garrison's last ability is resolving. No player may take any other actions between the time you make this choice and the time at which you draw cards.

If Minas Tirith Garrison is untapped as its last ability resolves, it can be tapped for its own last ability.

If an attacking Human is tapped for Minas Tirith Garrison's ability (perhaps because it has vigilance or it was untapped after being declared as an attacker), that Human remains an attacking creature.