I am an English businessman.

The way you're supposed to sign off a letter depends on how you start.

In a letter, if you don't know the name of the person to whom you are sending the letter, you start "Dear Sirs,".  If you start with this form, it is correct to end with "Yours faithfully,"

In a letter, if you do know the name of the person to whom you are sending the letter, you start "Dear Mark,".   If this is a formal letter, then it is correct to end with "Yours sincerely," - though if this is an informal letter you can end it however you want.

With email the conventions are more recent and less clearly defined.  I often start with "Hi Mark", or "Hello Mark" (just "Mark," is a bit gruff) if I've already spoken with the addressee.  Most emails to me usually follow this format.  I usually end these emails with "Kind regards," though lots of people just use "Regards,"

I do use the "Dear Mark, / Yours Sincerely" format in emails if I'm making contact with someone for the first time.

Hope this helps...

As a trained teacher of English as a foreign language (TEFL), the rules are still the same as they were when I left school (50 years ago!).

The valedition "Yours faithfully" is used in cases where the salutation is "Dear Sir" or "Dear Madam" .

The valedition "Yours sincerely" is used in cases where the salutation is personal, "Dear Ian" or "Dear Mr. Blogs" .

The valedition "Your truly" is often used in the USA but almost never used here in England other than as slang meaning me, myself or I  (the meal was prepared by yours truly) but even this is quite rare.

Capitalisation for the valedition is the same as for any paragraph, First letter is a capital then lower case.

"Regards", "Kind regards", "Best regards"  and "Best Wishes"  have become very popular since the advent of email. I personally use them only in emails. Basically, they all mean the same but my personal gut feeling is that "Regards" is the most formal and used for first contact, "Kind regards" is still formal but used for ongoing communication and "Best regards"  remains formal but used when the person has become an acquaintance.  "Best Wishes" would be used for a friend.