1. If you only use one country, then set Multilocations to default country only, and set the map to autozoom. If you then have one listing at either end of the country, mission accomplished.
[I saw you had more than one country in your database]
2. I was suggesting to use the calendar widget instead of the search. Your visitors will be able to choose any date, simply, from every page where you have the widget.
Visit my (very rough) test site to see it in action: http://goldroo.net/
3. Not possible with GD. Would be very surprised if there is any plugin that will do that. Only way to achieve that is to go to Google maps directly and plot your route there.
Or go from one listing to the other and enter the address of the last listing as your starting point.