Yes, there is a boat launch on site. There is also a marina that has boat slips you can rent while you are there if you don't want to take your boat in and out of the boat launch the whole time. It's 50$ per week to rent the slip.
This is an awesome place! We go every year!
Yes, there is a marina right next to the resort. I don't know who you contact to see about launching, though. The office could put you in touch with the right person.
Get an answer from The Landing at Seven Coves staff and past guests.