1) I would install it back by the fuel tank. In reality on my Studebaker, it is in the *wrong* location (underneath the drive door area!) but it has never failed me under any conditions.
2) It depends on the type of pump. If you have a 'flow through' (vane??) type--I think the Carter P4256 or some number like that , is of that type??-- then you could add it in addition to the mechanical pump, as a 'priming pump'. (This same company also sells 6 volt pumps of the "priming" type--I would contact them for a further explanation of what they are offering). If you have a solenoid type, which I think this is, then it is a replacement for the mechanical type. My Studebaker does not have a mechanical pump anymore, just a blockoff plate. NOTE: for the look of authenticity, you can retain a mechanical pump with the cam arm cut or removed, and the gas line routed through the pump. With a hidden switch, and hiding the pump, no-one but you would ever know. I didn't bother with this as I received the car in the shape it is in, and it has only ever been a driver. As long as it works, I won't fiddle with it. (only modify an existing mechanical pump that is completely trashed and needs a full rebuild anyway--don't waste a good core)
3) is the same as 2--it depends. Mine is on all the time when the key is on*
4)* This can be a problem, and if doing this as a full time pump, for goodness sake put an interrupter switch in it!!! EITHER have it die when the oil pressure drops (ie, with a separate override button for starting and priming purposes until oil pressure is established) OR have a 'bump' type switch that I think some modern Fords had in the trunk, that you have to re-set manually.