Every archer need 50 leadership, so 50 archers = 2500 lds.
But you dont need to have so much to take them to Rusry anchor and finish that quest. Just buy as much as you can and place them in 1 reserve slot, and then buy rest and also place them in reserve. Do same thing with pirates/robbers because you just need to have those units with you and quest will be finished, no need for any of those units to be in some of your 5 active army slots.
Good luck
