I'd say he should be happy to play varsity as a Freshman, even if he sat for half the games. My one bit of advice is that he should learn to really play first base and not just be a guy playing there because he's athletic enough to. Worst thing for an infield is a "just another guy" at first base. Understand that in a coaches mind, and basically every one whose a baseball person, if the ball bounces within the semi circle that can be drawn while in your stretch, it's basically considered the first baseman's fault if he does not come up with it. not a bad throw by the shortstop, third baseman or 2nd baseman, but the first baseman's fault for not getting it.
Take pride in playing one of the more important positions in the infield and become the best first baseman the teams ever had. Learn your defensive responsibilities before the coach has to teach them.