Some D III coaches do offer a guaranteed roster spot as a freshman; if that's offered, it's a good indicator. Every year, you'll be competing for a spot on the field. My younger son was hon. mention all conference last spring as a freshman, but if he had floundered this fall (he didn't), he would be in a big dogfight for playing time. He still has to constantly show he will contribute to the team's chances of winning. College coaches want to win games, and will play the lineup that they think maximizes their chances. Third parties (players and parents) may disagree with their assessment, but that's the way it is. There's never a time a player can relax and cruise, that's not how the game works. Max effort, every day, every game, every opportunity.
You've been given lots of good advice. Talk to the players that show you around, look at last year's stats and box scores to see who is returning where, how they did, how they finished, what class they're in. Ask the coach how things look at your position-he's been through the fall and has a pretty good idea of who will start opening day (less than 2 months away).
Good luck, and have fun. Despite the ton of hard work needed to get where you want to go, it is still a game and being able to play at the college level in any sport is a blessing.