Learn English – What does “off to” mean

As stated by drm65, making a buck off something does mean making money off it.

In the example you gave, there were people who were about to

make a buck off fearmongering about the 405.

Having just read a version of the article, there are quite a few businesses mentioned to be cashing in on the situation. (Many of the businesses are using the opportunity to increase business by targeting their advertising, or offering discounts to the many people who have chosen to stay in, rather than travel, during the highway closure.)

With regard to the word buck meaning money (or specifically, a dollar), I think that came from the idiom pass the buck, which originated as poker terminology. This is what The Phrase Finder had to say on the topic:

Players were highly suspicious of cheating or any form of bias and there's considerable folklore depicting gunslingers in shoot-outs based on accusations of dirty dealing. In order to avoid unfairness the deal changed hands during sessions. The person who was next in line to deal would be given a marker. This was often a knife, and knives often had handles made of buck's horn - hence the marker becoming known as a buck. When the dealer's turn was done he 'passed the buck'.

Silver dollars were later used as markers and this is probably the origin of the use of buck as a slang term for dollar.

"off the top" in general and here means the first 5 hours

In "off the top of my head" it means the first idea that came into my mind. Similar principle