What kind of factory ballast does your boat have? You will most likely need more than that 750 in ballast for surfing . You'll want to have some bow weight, as well as the port or starboard side and the rear port or starboard corner. Play with it and see, it may take a few sessions to get it all dialed in. There are at least one or two guys in here riding the newer VLX's, hopefully they can give you some advice as far as ballast setups.
A rope around 20 feet in length would be ideal, but I would go out and test first. Once you get you wake dialed, then you can know the rope size you are looking for. Its always nice to have something that you can shorten or lengthen up if you have to.