As some of the posts above alluded to, I think you're confusing what the Division means as it applies to academics. If you are a less than average student, D-3 does not mean less than average academics (nor does it mean less than average athletics).
For sake of example, Johns Hopkins, Amherst, Tufts, Pomona, Emory just to name a few, are amazing schools academically and play some pretty decent (D-3) baseball.
The quality of any given baseball or academic program varies from school to school, regardless of division.
While certainly there is an overall difference in quality of play from Division to division, typically in the depth of talent, especially pitching, for the most part the biggest immediate differences are no athletic scholarships in D-3 and a D-3 program will play about 40 games and a D-1 plays about 60. Typically, too, a D-3 team probably would not travel as much. A JuCo will probably play far more games than a D-1 program as most have extensive winter ball schedules.
In terms of the time you will put in, the demands upon you, etc. etc. I don't think the Division matters much. IMO you need to look at the particular school/program not simply its level/division.