They call them GarLeak gaskets for a reason. Make your own gasket for $5 and then use Permatex gasket maker 26B. It's the best way to go in my experience.
On a switch. This is just my opinion. Run a single ground wire out through the firewall to the relay from your switch. That way if the wire rubs or chafes the default of the pump will be on. If you run a power wire and it chafes..the fuse blows and you have no pump until you fix the wire. It's better to make it come on if there is a problem than off.