nshanny73's post in Treasure Map Capacity? was marked as the answer
I read somewhere, it may have been on this forum, that the max is 30 maps.
From personal experience, you cannot have duplicates in your satchel. I had Hennigan's Stead Central in my satchel and then was also rewarded it as a rankup bonus. I was unable to claim it from my delivery lockbox until I had claimed the one in my satchel.