Jake,
Welcome to the High School Baseball Web!
To answer part of your question about the stats: For D3, the HS batting average would be .600+.
THAT'S A JOKE!
I said it just to illustrate a point - HS stats do not really tell you what level a player can play at in college. My son batted .600+ his senior year of HS and is now a D3 pitcher and does not bat. But he attended a small HS and his stats there were from competing against inconsistent competition - some good pitchers and defense, some not so good.
So, how does a HS player determine what level of college they can play at? You'll find a lot of answers to that question if you read through the posts in this forum. Also check out some of the articles on this page:
Choosing a collegeBut for starters, it helps to participate in some regional or national showcases or tourneys and see how you stack up against a larger sampling of competitive HS players. I'm sure some other members will have helpful suggestions for you, too!