As long as there is a way around a trap they will avoid it.
You can only interact with visitors that have a question mark next to their heads. Select colonists with the best social skill and right click on the visitor that has the question mark.
Yes, I usually rebuild significant portions of my base as the game goes on. Especially to replace wood walls with stone walls to make the base less flammable.
You can’t shoot from within the walls. For cover To Shoot from Build sandbags. The best defense is to leave away into the base that is lined with traps and ends in an area with turrets and a shooting position for your colonists. I posted a picture of a typical entry trap above.
Wooden walls are of limited effectiveness since they can be torn down easily. Replace them with stone walls as soon as you can. Once your initial wall is built when you have the resources to do so double or triple it up.