I would be starting in <5' casting cleos and spinners to shoreline structure like boulders and overhanging timber. Trolling sand flats with wabblers and the like behind smaller gangtrolls can also work well. How clear is the water? No reason the splake should be any deeper than 20' during ice out period. They also really, really like worms so if you find an area where you know they're holding but have lockjaw that should do the trick...
As for the rainbows, wait until the water gets a little warmer and just flatline small spinners across the surface of the deepest basins in the lake!