Nathan, it sounds like you've already made your mind up, so why don't you build a 'final' version and see if you can sell it.
You'll realise the pitfalls as you go through the process. You'll learn loads!
If you post on here, we are all going to say strap a gardiners backpack on a cheap trolley (because we all know it works).
I used a Pure Freedom trolley for a year or so. It was very good but hard work, so I stripped all the bits out and built a van mount (obviously with a new battery).
I gave the trolley to my son in law (ex window cleaner, now funeral director) and he built a fantastic trolley, just to clean his own windows and soft wash his house, patio etc; he was bored!
Give it a go mate.
Personally, if I had all those hours to spend at night, I would learn about internet advertising: Facebook advertising, Google Adwords, Google Business Plus, etc. And I mean LEARN. That's where the money is!
Good luck.