Mark Appel will be on a pitch count, and the Astros will release his schedule start by start. But professional baseball is about to get real for the No. 1 overall pick of the 2013 MLB amateur draft. Appel is scheduled to make his debut Friday when the short-season Tri-City ValleyCats host the Lowell Spinners in a New York-Penn League matchup at Troy, N.Y. Appel recently threw a side session at the Astros’ spring training complex in Kissimmee, Fla. His heavy workload with Stanford this year has the Astros reluctant to push the righthander too hard during the remainder of 2013. But simply having Appel, a native Houstonian, on a pro mound is a key step forward for the 21-year-old and the Astros’ long-term rebuilding plans. “Tri-City is going to promote it, and hopefully fans will come out and see him,” Astros general manager Jeff Luhnow said Tuesday. If Appel stays on target, he is expected to be promoted to low Class A Quad Cities and could reach Class AA Corpus Christi before the season is complete.