I have a few usage questions for the forum. Some may not be incorrect because of any rules, but may be more style issues. I'm not really sure and would like some opinions. If you reply could you state specific grammer rules or explain the style issue involved? Thanks everyone!

What is the correct way to say this sentence?
"Do this with a keyboard hit just like the examples and the book code does it."
OR
"Do this with a keyboard hit just like the examples and the book code do it."
Is it "do" or "does" and why?

"What is the speed of dark?"
"What is the speed of darkness?"
I read the first of these sentences in L.M. Boyd's column. What is the difference between the two? Is either one incorrect? What does the ness suffix connotate that the first doesn't? (By the way, the speed of dark is the same as the speed of light. :) )

"He wanted to leave as quickly (quick, fast?) as possible."
Do useage rules say that I have to use an adverb here or can I use either "quick" or "fast" without breaking any rules? Do any of the options give the sentence a slightly different feel or meaning?

"It is that one pitch in a thousand you see in slow motion; its wings beat (beating) slowly as a hawk's."
I read this sentence somewhere and wondered whether "beat" was correct or whether it would be better to use "beating"? Is one way or the other more correct? What's the difference?

"My index finger hovered over the trigger, brushing (brushed) against it, caressing (caressed) it as I contemplated what I was about to do."
Possible changes to this sentence are in parenthesis. I'm not sure if the original sentence is correct usage or if it just gives the sentence a more immediate feel. But in that sense should I also change "hovered" to "hovering"? Should I keep my ing's and ed's consistent or does it really matter? Is there any rule that states whether I should do it one way or the other? What is the difference bettween the ed and ing suffixes and what different meanings do they bring to a sentence?

Thanks again for any help you can give me here. No matter how much I read about grammar I keep coming across or writing sentences where I'm not sure of correct usage.

Thanks,
Josh