The best piece of advice I received for my kid who is now a High School Senior is to make sure his Grade Point Average is as high as possible. Going into high school, we knew he wanted to play college ball, and we had no idea what level of college ball he’d end up being good enough for... what was clear though, was that a high enough GPA would enable him to get academic scholarships
This is great, GREAT advice. Something that I wish somebody had drilled into my kid's head (and mine) is that pulling straight A's in middle school does not mean that you'll do the same in high school with the same amount of effort. It is usually MUCH HARDER and takes more time, and you have to be ready for that.
Plus, in 8th grade the difference between straight B's and straight A's is that with A's you might get a ribbon or a certificate at the end of the year. In HS the difference might be getting into Stanford vs getting into Samford.
As for specialization, all good advice above so I'd just say that unless the kid can really mash I'd be leery of spending too much $$ and effort at C. The last person you want to be on a HS baseball team is the backup catcher.