As Kev says, its going to be obvious if you have a broken rocker when you come to start the engine. Its a bit of a risk whatever you do but from where I am sitting you are more likely to create problems for yourself if the injectors don't come easily. I'm afraid one of the things that only comes by experience is knowing how hard you can hit/pull/pry etc on parts to be safe. You need the car for Sat so I would say get the water pump, tensioner and belt on and tensioned. You can leave covers etc and the aux belt off and then start engine (dont forget the lockinhg tools). You will then know if there is a broken rocker. I personally don't think so as on your video the noise was fading in and out consistent with the timing drifting as you rev the engine. Don't worry about the lack of marks on the new belt. However, before you start the engine double check timing is OK ie once you have tightened it all down, remove tools, then rotate the engine a couple of times. You can then check the tensioner marks are correct and replace the cam lock tool. If the crank lock tool still lines up then you are good to go.