Powering LED and DC motor with USBC PD
As long you are within the limits, I don't see why it wouldn't work.
Negotiating on USB-C is not easy though, you will need some specialized chips and they are still sparse as USB-C is fairly new, not all stacks are implemented, that is the most tricky part of this project.
Be careful about the inductance of the motor, I don't think USB-C is designed to supply current to inductive load so you need to make sure that kickbacks aren't going to be a problem. If you have a step-down converter it should negate the problem though.
It makes more sense to have them in parallel as you will have fewer losses on the DC/DC converters and will need a smaller size.