essential: nonsense
comma: optional

Troll or joking?

IMO "respectively" is not essential, but is used as a formality.

The exclamation points are what add "intensity."

Cinzia is correct. The original text is ok.

"Within seconds, someone was doing something."
"Within seconds, someone had done something."

Both are possibly true. If the writer wants to convey what was happening as opposed to the results of that thing that was happening, it's the writer's choice.

I think that the sticklers for never splitting an infinitive were a few of the very old teachers when I was still very young, and I'm almost 50 now.

My guess is that it's just an old rule that few adhere to now. "To boldly go" sounds better to most people than "To go boldly." And I'd bet you'd find that example all over the Internet if you searched.

go to miss manners.

In general, in writing, avoid pronouns when confusion is possible or if the object of the pronoun has not been earlier named in the same paragraph or has not been named recently. Always consider if the reader could incorrectly assume you meant Joe when you really meant Tony or Adam in a context where more than one "he" is possible. Even when which "he" is obvious to you, it may not be to the reader.

I disagree with ngmacmillan's take based on reasoning stated by Mike and others.