Is it acceptable to close our business letters by "Thank you & best regards" as one phrase? Isn't it a very long closing remark?

It's certainly acceptable, but it is a little long.   I usually put the thanks in the previous paragraph.

"If you would be kind enough to answer my question, I would be most grateful.  Thank you.

Best regards,"

Hello!

Way back in Bangkok, an American teacher friend told me that we Filipinos tend to be very so overly way too much (duh) polite with our greetings and closing remarks when it comes to writing business letters. As I checked her advice on this, I found her correct at some point.

First, if the letter being wrote is really that professional, it should not end with very endearing remarks, for this negates the point of being professional.

Second, you may end with just half of this, saying "thank you," or just "best regards." In business letter, they tend to mean the same.

Third, if we read closely most of the professional letters we get from our heads, some of the really good writers don't mention "thank you" and "best regards" in one phrase, or sentence. This validates number one, professionalism wise.

Fourth and last... this is on me... If we still want to stand out as the polite and respectful Filipinos that we are, it does not matter if we add either a "thank you and best regards," so long as we are writing emphatically and the letter is intended to enlighten the mood of the receiver even if that is a business letter. It is also one way of building close partnership!

Thank you and best regards!

It would depend on the person you are sending the letter to and the content of the lette.

Also, you could use "warm regards" alone, again depending on the relationship and subjeect matter.

Yes it is acceptable, but it is usual to shorten the phrase as: "Thanks, best regards", which is the same as Thanks you and best regards!

sure, my dear brother there are certian things in the English language turns to be a formula to get some thing done specially in the writing phase and this is one of the many things you would notes