Learn Hardcore Japanese: tegami wo okuru mae ni, huutou to kitte wo zyunbisuru. - Before sending a letter, I prepare an envelope and stamps.

This pattern attaches 前に to the plain (dictionary) form of a verb to create a temporal clause meaning “before doing X.”
• 手紙を送る前に literally means “before sending the letter.”
• It’s a subordinate clause that sets the time for the main action (封筒と切手を準備する).

Can you explain the difference between 前に and 前で?

Yes.
• 前に marks a point in time (“before X happens”).
• 前で marks a physical location (“in front of X”).
In our sentence we’re talking about time (“before sending”), so we use 前に.

Why is the order 手紙を送る前に instead of 前に手紙を送る?

In Japanese, adverbial/time expressions (like “before sending the letter”) typically precede the main clause.
• 手紙を送る前に、封筒と切手を準備する → “Before sending the letter, prepare an envelope and stamps.”
• If you said 前に手紙を送る, you’d be making that the main clause (and lose the link to “prepare”).

What’s the function of the comma (、) after 前に? Is it required?

The comma:
• Separates the time‐clause from the main clause, making the sentence easier to parse.
• Reflects a natural pause.
It’s not strictly mandatory; you could write 手紙を送る前に封筒と切手を準備する, but the comma often improves readability.

Why do we use と in 封筒と切手 instead of や?

• と connects items exhaustively (“A and B” – you need both).
• や lists examples non-exhaustively (“A, B, etc.” – you might need other things too).
Since you need both an envelope and stamps to send a letter, と is appropriate.

Why is there only one を after 切手, covering both 封筒 and 切手?

When you have a compound object linked by と, you attach the object marker を only once at the end:
• 封筒と切手を準備する
Placing を after each item (封筒をと切手を) would be ungrammatical and redundant.

What level of politeness is this sentence, and how could it be made more polite or more casual?

• It’s in plain (dictionary) form, non-past – neutral or casual writing style (e.g., instructions, to-do lists).
• To make it polite: change 準備する → 準備します
“手紙を送る前に、封筒と切手を準備します。”
• To sound more casual/colloquial: use 〜しておく or contract 準備しとく
“手紙を送る前に、封筒と切手を準備しとく。”

Why is the subject omitted? Who is doing these actions?

Japanese often omits subjects when the context makes them clear. Here, the implied subject is:
• I, if you’re writing a personal note (“I will prepare…”).
• You, if it’s an instruction to someone (“You should prepare…”).
If you need to specify, you can add 私は (I) or あなたは (you) at the beginning.