You would really be best to start at Station Square / Duquesne Incline parking lot and not the actual point. The parking lot is directly across the river from the point and imho, one of the best places to view the city in the region. There is free parking at the lot, if you have people dropping you off. Assuming the trail is finished in April, it will be a straight shot to Mckeesport from the parking lot.
April is too early in my opinion. The trail could still be mushy from the winter melt. The project to complete the last bit is due to complete in April but it has been delayed many times before so it may not be finished in April.
Post back when we get closer in. If I have the day off I will be happy to show you around the city, including taking you to our bicycle museum (assuming I have the day off). I also have a detour for you if the path is still not complete. You are welcome to stay here the night before, if I am in town, just PM me. I live very c;ose to the airport if you are flying in. Actually you have the option of flying in, then jumping on your bike and take the new trail from the airport to the Montour trail. There is a campsite a short distance from the airport (maybe 8-10 miles). The Montour would bypass the city entirely but add about a day to your trip.
I just got back from a conference in Orlando. It looked to me like a pretty ugly place in which to ride. You are going to be blown away by the beauty along the GAP.