To size the motor you need to work out what continous power you need to drive at cruising speed. Then select a motor which has a rated continous power above this calculation.
So you need to determine your aerodynamic (cd and frontal area) drag and Rolling Resistance
(this should be a minor component) and choose a cruising speed.
There are spreadsheets available on this site to work out the continous power then needed.
If you live in a hilly area then you should work out the incline, speed of ascent required, and max laden weight and see if this affects your continous power rating.
Folks (not me!) here could help selecting a forklift motor candidate once you know your requirements.
Or get a warp 11.