Waypoints will force the path to where ever you want, so use them. And if you want trains out from the depot to both directions, it’s easiest to do 2 depots. Or, simply place the depot at the end of the platform on the last stop on the line.
Since the auto update feature, i’ve never returned any trains to depot anymore.
One way signals on right places and waypoints work wonders. And build bigger stations and avoid using the same platform for more than 2 lines.