A dash cam typically is only activated when the officer's patrol car lights and/or siren are activated. A routine business check would not require the lights and siren to be on.
A body cam would not always be on, it would most likely be activated by the officer when he is responding to a call or has some reason to believe that something was about to happen. Once again, the first issue here is not in play. We do not know right now why he approached these 2 men, they might not have appeared suspicious, maybe just loitering and he may have been asking them to leave the area (I do not think that would require the body cam to be turned on, unless there was some greater issue). Now, if he saw them smoking weed, brandishing a gun, if they appeared to be someone that he knew had an active warrant, or so on, then I would think he would have activated the body cam (assuming that he did in fact have one).
I am not commenting on them not allowing him to get medical attention, because that has nothing to do with the things I commented on.
There is a video here that shows a distant view of the incident, but does appear to show the suspect raise a gun at the officer
http://www.usatoday.com/story/news/nation/2014/12/24/man-shot-killed-berkeley/20849045/
Also, to your 2nd point, from that same article:
The body of the young man remained on the scene for about two hours, Belmar said. After Brown died in August, his body remained on the street for more than four hours, an action that drew widespread criticism.
Belmar said two hours is fairly typical as police gather evidence, and interference from protesters may have prolonged the situation in Berkeley.
