The fitting on top of the tank is probably for a vent and the silver fitting is the vent itself. It would be connected to the elbow with a hose and located significantly higher than the tank. However, if you already have a vented fuel cap you can just plug the vent opening on the tank.
Yes, there should be a pickup tube in the tank. The gasket should be ok as is but some sealant is ok if that is what you wish to do.