I'm glad your wanting to get started on something like this but your aiming to high. Start with a cheap cruiser Schwinn with coaster brake (not a new one)
Buy a 110$ eBay 2 stroke. Sell it for a profit.
Nothing else. No engine upgrades. Nothing. If you do then you won't be able to make as much profit. And there is nothing wrong with a 110$ eBay kit.... I still use them. Decently reliable (you still have to work on them. They are a 100$ engine don't expect much) I've rode a 25mile trip one way, full throttle and a lot of hills. Only problem was having enough gas to get back
I did a 50km trip last night. WOT all the way except a few steep downhills where I shut off the engine and some woods road sections where road was too rough for 60kph. Didn't come close to using the tank of fuel, maybe less than half. This is more than 10 tanks of fuel, I am on my second 20 L jug of gas in this bike. No idea on how many miles overall but I think it has established reliability.
$50 used bike
$200 GT5A motor kit
$32 aftermarket head
$20 quieter muffler
Some sanding and grinding to the original head and ports. Lowered the float level and needle. Perhaps 100hrs of tinker time?
$302 into this bike, does 55-60 kph, will manage any highway hill on its own power.
It seems reliable, now.
What you are not factoring in is the many years of mechanical experience and the hours and hours of time to get it that way.
I think you would be hard pressed to put a kit together in 4 hours. It will take most of a day for the first couple bikes, especially if you have to massage the exhaust pipe and file the mounts to fit. So what is your dollar per hour return? I don't mean to stomp on your dreams but the world is full of unknowledgeable failed entrepreneurs who take dozens of unsuspecting customers down their sewer of failure. LEARN! Do what you know. Bill Gates, Steve Jobs, and Mark Zuckerman were not kids that got lucky. They were brilliant, hard working and ambitious. They did what they knew best and had years of experience at it.
How many forum members have asked about tensioners slipping or low speeds or cracked tanks? These things are a result of poor mechanical skills and knowledge. It ain't just about tightening nuts y'know?
So when you make these mistakes and a customer's tensioner rips up the spokes and puts him in the hospital, what are you going to do about it? Hide behind a useless waiver?
Stupid hurts and it is not cheap. The risk vs reward is not there. Guys like KC Vale know their stuff, years of experience, beautiful builds and back it up with service. You do not have that ability. True knowledge is built from learning tested by experience. You have neither.
Start with a used bike (they are everywhere!) and a cheap 2 stroke kit and LEARN. That is exactly what I am doing. These bikes are a wonderful education, but you cannot sell "I DUNNO".
So what are you doing? Putting ads on Craigslist? For what? What are you offering? A dream? Vaporware?
I'd suggest if you had taken that lawnmower and rake door to door like I did as a kid, you would by now have the money to buy a cool powered bike.