Seneca River is supposed to have lots of crappie. One member here caught a ton of them near Plainville here a couple weeks back. The weather here has been screwy too. Water temps up and down.
I think you'd be OK hitting the Seneca between Montezuma and Mosquito point (Haiti Island). Any bridge abutments, or back waters around islands can be good. Look for submerged wood too.
For launcing, there's one in Montezuma, almost across the road from the refuge main entrance. I've never used it, so don't know how good it is. There's another DEC launch on Rte 38, north of Port Byron. That one is a Concrete ramp and has a dock.
Late May to early June, I'd expect them to be in a post spawn pattern, working into a summer pattern.
For Rochester info, you might want to join up at WayneCountyBass . Yes, it says "bass" in the name, but the gang fishes for everything, and the membership is pretty much geographically centered on the Rochester area. A good place to hang out to talk about local fishing.
Good luck when you get up here, and thank you for serving our country.
Joe