You should be able to scroll the map with the mouse near the edge of the screen. It works for me. If not, I'm not sure why.
Only units with a backpack can pick up loot. The scout and the rogue are the only ones with a backpack. Scouts, rogues, and bounty hunters are also the only stealth classes, so they can sneak by enemies for a short time. This makes it easier to scout the map with them. Also, they can backstab for extra damage if a unit is caught unaware.
Retire is a permanent action. When you retire a unit, he is gone, so all materials you used to make him are wasted, and any money you spent upgrading him is gone. It's basically a way to "save" a unit that you can't get to since there is a strict population limit. You will have to create a new unit once a unit is retired. If you click retire, it asks for a confirmation, then the unit returns to the tent and disappears. If you saw anything else happen, let me know.
I wrote descriptions for most units and resources to explain most of this. It takes some time to absorb all the rules. I can try to make them more clear as I get more player feedback and see what people are missing. Hover your mouse over anything in the UI. All units, resources, and button generally offer some kind of guidance.