Hi. Interesting project. I recently finished a project for a small cardboard sprayer. This system used a step motor to handle the spray head. In addition, it consisted of two pumps, one for the treatment liquid and another for cleaning, as well as two valves. The interaction with the sprinkler was done with a Nextion brand HMI used to introduce the parameters of speed, maintenance, alarms and the handling of buttons like ignition and stops among others.
I do not know the dimension of your machine, but if it is something big and robust, it is necessary to use a servo.
I would like to know more details about how you want to control the engine, the starts and stops, speed control, torque, etc.
I recommend the use of some lcd screen for the interaction with the machine. It could be a nextion brand due to its graphic quality and versatility. The connections with the arduino are very simple (only 4 cables via serial).
I recommend the use of opto-coupled relays to avoid interference and electrical noise from the motors to the arduino. For this there are modules with optocouplers included.
For any comments or questions, please let me know.
Regards
Darwin P