I've been there often (I grew up in New Braunfels and my parents still live there). We were there last weekend at Comal Park in fact. Comal Park only has one boat ramp open and no courtesy dock available. That means if you want to go to party cove, you'll have to beach your boat in the mud which I highly suggest you avoid. You might want to try Skyline Park/Canyon Dam. Although there is no beach or swim area, I'm 99% sure their ramp is open and they might have their courtesy dock still operating.
GET OUT THERE EARLY!
We arrived at 7am and had a blast until about 10. It was smooth water and there was very little traffic (see pic below). After 10 it was okay, but if it gets too crowded you'll be toobing or going home early. If you want smooth water, stay in the coves for sure, just don't get too close to the islands as they're not always there and can be very shallow even when you're not right on top of them. I can't tell you which coves will be best because I don't know which way the winds will be blowing that day. We always go out there and just cruise until we find a nice spot.
I believe the restaurant Nate talked about is Baja BBQ Shack, I was there last weekend as well
It's pretty good. Typical restaurant food with a pretty laid back atmosphere. They have slips just for their customers which is awesome.