Your questions are a good starting point. My son is entering his last year of HS. He committed spring of his sophomore year. It's hard to be specific, we don't know you, your son. Even if we did, too exact of a roadmap could lead you astray.
Here's my best summary advice. It may come across jumbled, but here you go.
Listen to everyone but make your own decisions. Keep your relationship strong with your son. No path that strains your relationship is worth it. This has to be your son's journey and not yours. Keep encouraging your son to play multiple sports, but don't make it a requirement. Read a lot, especially with regards to strength, conditioning, agility training. Keep learning and encourage your son to keep learning. Follow Eric Cressey, jaegersports, college baseball athletics trainers on twitter. Always seek out the best competition for your son in lieu of showcases, camps or "events you gotta play". If at all possible, make the high school experience a big deal. And "Enjoy the Ride"!
The path, luck, chance, set of right decisions or whatever happened on my son's journey may be the exact opposite for someone else and both may still wind up at the same place.
In addition, stay with this board. Pick out a few posters that have older kids that have been through the process and reach out to them with specifics with the PM function.
Good Luck!