You need double insulation on both sets of tracks where the tear drop is. Thats 4 insulators. You should have the 2 sets of insulators separated by enough space to have the entire train in the reversing area, while you change the direction control for the rest of the layout. For operational purposes, you MUST be able to change the direction of the layout while the engine is TOTALY within the reversing block. To avoid potential shorts caused by cars that are lit (caboose, pasenger cars, etc) they should also be in the reversing block when you throw the directional control.
Where the switches are, you need the direction of both hookups to be the same when your engine crosses over the insulating gaps, and you need the same rail to be positive, and the corresponding other rail to be ground. It would make sense (?be required???) to hook up your positive treminal to both upper rails, or to both lower rails