I would suggest chocking all wheels on any engine start especially the first one, and have someone at the controls / brakes. It looks like the tail is tied down, the rope looks pretty light. If it went to full throttle you could have a runaway plane on your hands. I realize this is a 100+ HP engine, but stranger things have happened.
Also, having the prop blast pushing into the hangar will cause a lot of dust and debris to go everywhere and come back into your air intake.
I hate to keep looking for safety issues, but starting the engine with the tow bar attached is real bad karma.