When closing a letter with the following, should 'sincerely' be in capital? And should there be a comma after 'sincerely'? Thanks.

Yours Sincerely/sincerely,

I learned 'yes' to both your questions.

Sincerely yours,

or

Yours sincerely,

only the first word in a closing should be capitalized, as it is really a phrase which is part of a sentence.