Too bad there are not more owners out there to answer your post. There are a couple in this marina and their experience would support the position that Elect drive is not for everybody.
Here is my 2 cents:
There is no extra power. If you do not have a diesel gen to recharge your batteries will slowly die unless:
You have only short sails and the boat is returned to the dock for charging from the grid.
You have only long sails, days in length, and good wind.
You have a very short power use to get out of your slip and only sail on days with good wind.
I would suggest getting a larger motor, smaller bank and diesel gen large enough to drive your boat at cruising speed.
Better yet wait for a turn key system. They are coming they just are not here yet for less than big money.