I can only speak for myself.
I would think you will have a budget that you have to work to.
I am into early steam Tugs and for that I would need a multi pole, high torque, slow revving and ball raced motor.
The prop has to be in Brass and of the right type for the period.
Prop shaft, it would be a good idea to have an oiler, threaded at both ends, a good coupling, may be an alignment tool.
Electric Speed Controller, they have to be suitable for 6 volt and upwards, and of good quality.
All the components and linkage for the fixing of the rudder
That is only the starter for me, there would be more things that I would like in a kit, but that would just push up the costings.