Competitiveness varies by school - some HSs are starving for players each year while others cut dozens every year. Check MaxPreps to get a sense of the historical W-L record and league standing for the schools you are considering.
Can't hurt to play on the feeder teams, but the level of 'required-ness' is up to the coaches. Ask around. People love to chat.
If your son wants to play in college, he'll need to keep his skills up during summer and fall. Summer is also when colleges come out to see potential recruits play.
But, one step at a time. No one is recruiting 2028 grads quite yet. Good luck.