Posted this elsewhere, but throwing it out there for general consumption/disagreement/hole-poking:
1. Hoid is on a mission. (first letter)
2. Lots of people are hunting him down. To stop him perhaps? (first letter)
3. He rejected the OGs that took out Adonalsium. (Secret History)
4. He is gathering items of investiture like the Lerasium (Secret History)
5. Connection to a shard is required to hold a shard. (Secret History)
Theory Time: Hoid is collecting all the goods so that Adonalsium can be restored (H/T to others who I've seen posting versions/aspects of this). The In-Cosmere 17th Shard is working to prevent the restoration of the shards. Where I differ from other similar theories is this: I don't think he wants it for himself. He wants to sucker some hero into taking them all. "Here, eat this bead, just eat it. Oh, and here is a flower, trust me." He'll make someone a perfect candidate to hold all of the shards. My vote is for Stick.
I'm going to go back to lurking now. Enjoy.