If they were multiplayer, I would be. That's the most important bit for me. Raiding, trading and roleplaying.
Perhaps carrying items would be a useful idea. Backpacks and pouches, that sort of thing. With nothing equipped, you can carry very little, which makes sense. You could have a few different sized backpacks for carrying different amounts with maybe a speed penalty. That would be interesting for trading/raiding. If you want to trade safely, then you need to do low volume so you move quickly or large scale with many wagons and a guard escort for safety.
I agree limiting the NPCs trading capacity is a good idea. Perhaps caravans can only be formed with a player present to escort from point to point and without a play only individual wagons can be sent. I think players may be a big enough threat to trading, but NPC robbers would be interesting as well.
How many people are working on this game with you?