Beauty, to Herrick, is in the world, and it is only temporary. To describe this sentiment, he uses the daffodil:

The “Fair Daffodils” don’t last very long, anywhere from six weeks to six months, although in Herrick’s native England it’s like as not closer to the former. To Herrick, the death of this beauty deserves mourning.
http://www.youtube.com/watch?v=dpDMBEVmRac

In light of the preceding line, this line is ironic.
For one, driving slow – in the literal sense – is a good way to avoid being a part of manslaughter while driving: handling your vehicle carefully makes the driver less liable to be involved in an accident.
While taken contextually, careful choice of words to convey a message – “vehicular verbiage” – is the surest way to murdering the track. Manslaughter is defined as the killing of a human being that is less culpable than murder in the eyes of the law – so being a part of manslaughter isn’t even murder.

However, it is still killing a man, and it seems as though this is what J-Roc’s pointing out (even if it is laced with irony): if you’re careful and particular in your word choice, as with the last line, you’ll kill the track.

Indirectly, this reflects on rap as an art form – if the rapper’s “killing of the track” is murder/manslaughter, the track is a living thing, a creation of the artist.

This line is dope.
“Vehicular,” here, is pertaining to “vehicle” as a medium of communication or conveying a message.
“Verbiage” is being used in a less common sense (see second definition), as a synonym of the word, diction, or word choice.

Basically, then, J-Roc’s saying that choosing the right words to convey your message is essential to killing the track. He also cautions the listener to “drive slow,” being careful and precise in word choice.

J-Roc could also be referencing Kanye West’s single off of Late Registration: “Drive Slow.” Kanye is a known perfectionist, and the slow tempo of this single reflects both the title and the caution and precision with which Kanye and his collaborators created it.

He feels like he’s been through everything life offers, except for death.

Ironically, you’re not typically ever in a coffin during your life, unless you’re – quite unfortunately – buried alive. Going inside a coffin while still living is actually common in two Asian countries, particularly when compared to the United States:

http://youtu.be/bVX3-hHnttU

• South Korea, for example, has “coffin academies” where you can experience your own funeral while still living. It’s intended as a tool to prevent suicide, which runs high in the country.

• Japan, on the other hand, doesn’t give you the funeral experience, but offers the opportunity to actually live in a space with a volume comparable to a coffin in aptly-named “coffin apartments,” which can rent for an equivalent of $600 a month.

Commercial wrestlers and MMA fighters often fight cage matches.

In the WWE, they sometimes fight special “Money in the Bank” matches, where you have to climb to the top to win the prize.

Diamond Dallas Page was a WWE wrestler from back when it was still the WWF (before the World Wildlife Fund sued).

“Bang!” is one of Page’s catchphrases.

Diamond Dallas Page runs with the above pressure metaphor. Ironically, Page eventually did bust under the pressure, quitting the WWE due to injuries.

J-Roc, on the other hand, isn’t about to bust; he’s going to climb to the top. CSF are bound to make a name for themselves.

High water pressure will often bust pipes…

While high pressure is also necessary to make diamonds.

The pressure of the rap game either makes you bust or shine, fail or succeed. Basically, you’ll either take the heat, or get out of the kitchen.