Here is how it works. Part 135 is very strict. The pilot is a 1099 contractor. Basically a couple of days in ground school learning part 135 and company manual and do a check ride similar to any IFR ride you have done and as long as you have 135 min hrs. The plane is another thing altogether. At our company we stick to 1 type as adding a new aircraft is an exhausting experience at the Feds. A single needs a fully coupled gpsss auto pilot, back up vacuum, back up alternater and a few min gauges etc. the engine has a 12 year cycle, meaning it need to be replaced or rebuilt regardless of hours every 12 years. Also the prop and governor only has a 6 year cycle. After you add the aircraft, you have no say in how it is operated. You will fly as an employee and basically you might operate at break even on the plane if you lucky.