I believe you would like to have tracks 3 & 4 for arrival/departure tracks. They could actually be moved closer to the yard for this purpose. That leaves 1 and 2 for your mainline. That makes sense because it will be the side you have your passenger trains stopping. You'll need crossovers to get from both north and south-bound mains to the arrival/departure tracks.
The loco service is not in the best place. You generally would like to cut off an engine in the arrival track and have a way to the engine facility without crossing the mainline. You'd like to be able to get an engine from the loco facility to the departure track in the same way. That leaves the area now showing as a street and buildings to serve as the area for the loco servicing facility. Perhaps you could swap that existing area for the loco facility.
Modeling the North Pennsylvania Railroad Bethlehem Branch in N Scale