Draw up the plan and surprise him with it on his birthday, but choose another month to actually celebrate his birthday with the trip. April here is ugly. It’s too cold to be comfortable, but too warm for snow. The plants haven’t started blooming yet so everything still looks bedraggled from surviving winter. Literally any other month is better (although November is pretty dismal and its only advantage is being on the front end of winter instead of the back). Late spring/early summer you will have to bathe in bug spray.

I don’t know that a train will get you where you want to go. There isn’t much in the way of trains here, and they go to populated areas. Probably should drive.

I hear a lot about Kingdom Trails for biking. Willoughby is close if you want to play around at a big lake and hike.

You can use Dark Site Finder to help find the best places for stargazing. (Cool-colored areas give you the best possibility for seeing the Milky Way, the cooler the better.)

I don‘t having any particular recommendations for restaurants. Variety and fancy places are going to be in populated areas, away from the stars, but you can find a place to go wherever you land if you aren’t picky.