I am under the impression that the majority of customers in India will be very price-conscious, so I imagine the most popular systems will be for lower speeds. High speeds require expensive equipment, and I really strongly recommend some suspension for higher speeds, for safety and comfort. For lower speeds this is less of an issue.
I read quite a bit, and I am under the impression that welding with steel is widespread across India, but...I suspect that heli-arc for building or repairing aluminium bike frames is less available. If this is true, then you would focus on a low-speed ebike with a steel frame that has no suspension. For the very affordable addition of a small amount of tubing, you can extend the rear of the frame to make a longtail cargobike, which I am certain would be very popular.
I believe that mopeds are very popular there, so a selection of moped rims and spokes should be available. For reliability and ease of maintenance, I would recommend a direct drive hubmotor in the rear. It should be a fairly large diameter motor, but mounted in a smaller wheel. A 16-inch moped rim will seat a 20-inch bicycle tire (just as an example of the size of wheel I am suggesting). If you are using a moped rim with angled spoke-holes, you can mount a common 9C/Yescom size of hub with a one-cross pattern.
Moped tires (at the heavy end of the bike) are very flat-resistant, and a moped rim of a certain size will seat moped tires, or a 20-inch bicycle tire. A DD hub is very reliable, and if you use a sensorless controller, you never have to worry about the Hall sensors failing. I would recommend a 36V battery over a 24V, even if customers want to save some money by getting the smaller battery.
"DIY longtail, could it be this easy?"
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