失礼します！　完全にリライトすればいいと思います。　すごく美しいことを書いていますから、美しく書けば良いと思います。

Happiness.

What is Happiness?

Many people, in the pursuit of happiness, find themselves obsessing over material goods; yet never pausing to question whether this brings them true happiness. Yes, I do believe that materials can temporarily fill the great void within, but only temporarily. This is why, in many cultures, we find this incessant consumption of material goods; people are chasing the fleeting glee found in the shadow of joy that the materials represent, yet never truly grant.

 

意味が変わっていませんけど意味がすごく変わってしまった。

 

During would indicate when/under what circumstance something occurred, whereas throughout would mean that it is continuous or reoccurring. For example; "Some time during last night, ambulance sirens were blaring and I was unable to get a good night's rest" This tells us that it occurred while the sun was down, and it doesn't necessarily imply that it was reoccurring or that it was in any way continuous. "All throughout the night, I kept waking up to the sound of ambulances and police cars passing by my house!" This one alludes to a night full of constant noises from cars passing by causing noise, because the word "Throughout" would tell us that there was a continuous disturbance that lasted the entire night (or the majority of it, or periodically throughout). Hope that helps.

LAI LAI HEI, by Ensiferum.

It really depends on what you're asking, and how you ask it. All of the words you provided have varying meanings, so I'll detail the slight differences. 1] can you: This one is asking if the person is physically, or otherwise capable of performing your request. This one is the least formal because it could imply that you believe the person is unable to perform a simple task. A:"Can you open the door?" B:"No, I'm paraplegic, and therefore cannot." 2] could you: This is also similar to "can", but it's a little more formal. Unlike "can", however, "could" is asking basically if there is a possibility that the person would perform your request. A:"Could you open the door, please?" B:"I could, but I won't " 3] would you: Is basically the most polite word to use, because it's very indirect. This is the past tense of "will", and can be used interchangeably with it in most instances. A:"Would you be a dear, and fetch me the paper?" B:"I would, if only you would say please, you heathen!" 4] should you: I'm assuming you meant to write "should". This one implies that there is a decision to make about whether or not something is a necessary course of action. Something that should be done is something that needs to happen. A:"Should I go to work today?" B:"No way, money is the root of all evil" Hope that helps.

やはりそうですか。　ありがとうございます。

Study every day!

"After" would be more proper from a scholarly perspective, like writing a paper. The main reason is because "after" simply has less meanings than "once" does, and it makes for easier translation. "Once" would be more appropriate when writing a short story, or fictional book; ex. "Once upon a time".