Learn English – What are direct and indirect objects to “provide”

Here goes is an idiom that is usually used to express determination or optimism at the start of a risky or difficult task. The implicit subject of goes would be the party taking the action--think of it as shorthand for "Here I go," "here we go," "here you go," etc.

For this reason, I would not use here it goes in that way. It is more likely to be used in a more straight forward way: "Now, which drawer should I put this fork in? Oh, here it goes."

In a passive construction with a participle like separated, by and with have different functions.

• by marks an agent phrase: The fighters were finally separated by the referee.
• with marks an instrumental phrase: The fighters were finally separated with a crowbar.

When you're talking about metaphoric separation -- item boundaries in a left-to-right line -- you have the option of treating the "separator" either as an agent itself, or as a tool (of another agent).

Interestingly, this is the same range of meanings as the agentive -er suffix:
a typewriter is an instrument, but a ghostwriter is a human, and therefore an agent.

• The entries are separated by commas is the agent interpretation,
  a passive version of Commas separate the entries.

• The entries were separated with commas is the instrument interpretation,
  a passive version of Indef separated the entries with commas.

Note the different tenses required above; being separated is either an event or a state. Permanent states normally take present tense (My car is red even though it's been red for 5 years). Events can be located on the time continuum, usually in the past tense. So past tense is likely to signal reference to an event, and present tense to a state.