Where does the $1782/month for Payment and Insurance come from? If you fly 60 hours/month (which is a pretty high average), that is another $30/hour. Plus, your markup of less than 10% is way too small.
A few months ago at my FBO, the FAA came out and "suggested" we replace all the plastic fairings on a 172 because of a few cracks. There went $2,500 just like that... You will also likely need to fly the plane to other airports for some of your mainrenance (extra$$$), unless you have avionics and everything else at your airport.
Also, there will be down time when you overhaul your engines, but the insurance and payment is still there. You could exchange and save lots of time, but that cuts out many of the lower cost overhaul options.
You may have a good idea there, just keep your prices high enough to make you some money and low enough to attract some customers.