Brother you are upgrading from a high maintenance car to another higher maintenance cars.
Just get the parts and servicing prices and get estimates of prices of clean low mileage cars.
If these cars go bad mechanical or electrically they will cost u an arm and leg.
Officially CL-9 needs high octane or greater than 90 RON. But any how people here have already installed CNG or either running with CAT converter removed.
Get a new civic instead its much better.