One thing you'll have to understand about Orchard Beach State Park in Manistee. The campground is on a bluff above the water. The only way down to the beach is a wooden stairway consisting of about 75 steps. Still, it's a nice beach, but if you're not into stair climbing I'd check out something flatter.
Platte River is a nice campground. The Platte River itself can be accessed fairly easily from the campground and is a nice canoe or kayak ride down to the big lake. The Platte River campground is fairly close to the Sleeping Bear Nat'l Lakeshore which can be great for dune climbing or sightseeing. The small town of Empire, along the way, has a nice little beach on Lake Michigan. BTW, just east of Empire, along M-72, is a nice private campground, Indigo Bluffs. It has a pool and there is a golf course across the road.
July is a very busy time along Lake Michigan. All the state parks are full or nearly full. Late June is also a nice time as temperatures can vary whichever month you go. Black flies aren't a particular problem along Lake Michigan. When I lived in the U.P. the black flies can drive you away from the beach areas quickly.
Ludington SP is extremely busy, especially in July & August. If you're planning to get into any of the Lake Michigan state parks be sure to reserve as early as possible. Use the state park reservations website to research potential sites (there are photos of campsites along with the lot size & levelness). 6 months out is the registration open period and many people are on their computers ready to jump onto sites of their choosing the moment they are able to reserve. Set up an account early so that it makes reservations easier.
https://www.midnrreservations.com/ Petoskey SP is on the water. There is a paved bicycle trail that goes by the park which you can access easily. The further north you are the cooler the big lake temps are unless we have very warm temps early in the summer.
If you have young kids or kids that are active you'd best shoot for Platte River. There are plenty of things to do around there. You can tube the river too. Even though I say this you can't go wrong at any of the parks you've mentioned. Besides, there's always next year.
