FYI Pier 121 is a members only ramp, thats the ramp I use. You want to use the one next to it if you're on that side of the lake. There wont be much riding to do on the weekend on Lewisville as it is packed with every type of boater out there, even in the morning. If you're just going to party cove then I would advise launching at Eagle Point Marina or even the ramp next to party cove which is West Lake Park, (heres a Google map
Party cove is a great time for some great "scenes" and just general foolishness. It usually starts bumping around 2:30. If you have any other questions let me know, Im usually out there twice a week so I know that lake well.