Some resources for rout planning:
http://www.buckeyetrail.org/ The Buckeye Trail is largely off-road hiking, I think, but it seems like it'd follow and perhaps overlap your route, and might have some camping options.
http://www.ohiotoerietrail.org/ The Ohio to Erie trail goes diagonally across the state. At 300 miles, it's rather shorter than the trip you have planned, but might be a good warm up, and it might provide some camping options at the points where you cross it (although I don't really remember seeing camping resources on the site).
http://www.ohiobikeways.net/ Has lots of bike trails that you may or may not want to work into your trip.
To prepare, you just need to get some miles in. Plan on low miles to start, or plan on optional early bail-out spots. If you're not camping, gear should be light, but planning might be tougher. Depending on the size of the towns on your route, hotels may not always be easy to come by. And if towns with hotels are 50 miles apart, you end up with not much flexibility in your route. It's one thing to get to your first lodging option and decide that you'd rather put in another 10 or 20 miles, but an extra 50 is a big commitment. I tend to do short trips where I can plan for every night's stop with reasonable certainty and with options for an early or longer day. But beyond a few days, it seems like playing it by ear would be more enjoyable. But it's hard for me to imagine playing it by ear in rural Ohio and not camping.
Also you might check some elevation profiles. Seems like sticking to the river should be mainly flat. I just remember that after spending a lot of time riding around NE Ohio, I was surprised by the hills I encountered when I headed towards the center of the state. North east Ohio had spoiled me.