IIRC D3's also have a limited number of fall practice days. For some reason 16 sticks in my mind. That's days the coach can run things - but he also relies on captains practices and (ahem) mandatory lifts with strength coaches. My son's D3 would end their Fall season w/ a scrimmage against a nearby D1 team - three 6 inning scrimmages. Might be the first time you see your son play all fall which is a very different experience for many (if a parent shows up at every practice, the coach will notice and figure out who you are.... whether it helps or hurts perhaps depends on the coach or maybe how much $$$ you could donate to the program ).
Like others have said - be prepared, work hard, keep your eyes, ears, and mind open at all times - never forget to watch your back. In the Fall, the freshman are the "next best thing" until they prove otherwise. Oh and next Fall, guess what there's a whole new crop of "next best thing's" showing up and the coach is all too happy to tell some lazy upperclassman to work harder because there's some freshman gunning for his position.