I think this is going to be a tough one to tackle from a design standpoint.
Do you trust that your game will attract and create a friendly and helpful community?
Personally, I kind of like how WoW is currently handling loot, for the most part. I am not a fan of personal loot being mandatory for everything as that takes the joy out of it. However, I like all items being trade-able for a short time after looting. I feel like it helps negate the instance of “oops I had that set to need” because you can then give that item to the player who needs it the most.
As far as farming gear to twink out alts, this is definitely something a vast majority of people like to do. I’m not really sure how it fits with what I wrote above though. Maybe items that you find while solo are not bound to the character that looted them, but instead to that player’s account?