If quote is created and user does not add to cart and does complete booking, do we need to decline the quote?

Yes, DeclineQuote should be used in this case to ensure we archive any unused quotes.

If quote is created and user does not add to cart and does not complete booking, do we need to decline the quote?

No,DeclineQuote is not required in this case.

How long before a trip can the weather quote be offered?

We can create quotes up to the day before a trip begins, though the odds of not being able to provide an acceptable offer due to high risk of bad weather does increase as the date approaches.