Well I am certainly no expert on the area but we where there all weekend with the Midwest Jet Boat Rally and we used the Chain O lakes state park and that is right at the Blarney Island area on Grass Lakes. We saw several big boats putting in at the park and the ramp had 4 nice slots with lots of parking and dock space.
When we left on Saturday night there was a 28 to 30 fountain putting in so the channel can handle your boat I think. I tried to stay in the main channel and my depth gauge read 2 to 5 feet most of the day in all the no wake areas.
Theh out of state 5 day permit was 25 dollars and some of us bought that right at the ramp in the park.
Good Luck
Randy H