I say make check in around 9-10am. That'll give the daytime guys plenty of hours to shoot on day one, and give the nighttime guys plenty of time to reach their destination and catch a nap. Plus it gets guys on the road at a decent time on Sunday. To get participation up, you have to attract those day shooters too.
Like I mentioned on my text, I'd keep the entry fee around $200-250/boat. You and I could afford a $500 fee, but a lot of guys won't be able to swing it. It'll scare off more guys than it would attract IMO. Do 100% payback minus fish disposal, and limit the big fish side pots to 2-3max. Maybe biggest overall, and biggest carp and buff?
Trailer anywhere, make it big 20 or 30, with maybe a prize for say $200 for a totally random drawing at weigh in. That'll keep guys coming back to weigh in who may not have had a good night. Put every team name in a hat who is present at weigh in, draw one out-they win $200.