It appears what you were actually doing was rubbernecking and blocking the only safe route, causing another crash. I hope that wasn't the case but that is how it appears in the video.
An insult rather than an explanation. That tells me all I need to know. I urge all drivers to learn from videos like this. Dont block escape routes. Get out of the way as quickly as you can, safely.
Get past an accident as quickly as possible , coming to a virtual stop wont help anyone and its just asking to get leathered up the arse by a clown like the Porsche wizzing by into the armco. Golf was lucky not to get collected there. I know there was a fair bit of debris but grass was pretty clear , self preservation got to kick in.
Depends on what the grass was like. It has rained alot recently so it could have sodden. As a marshal I would rather get through safely than risk getting stuck also.
Situation dependant, if conditions are dry and no cars ahead of you are moving then yes, but in this case he had to wait for the Golf to make a decision whether to go on the grass or not