Punctuation with particular adverbs, conjunctions

Please, I'd be very grateful to be enlightened about the correct punctuation in these particular instances. I've been wondering too long what rules stand for this, but I am not capable of finding any.

(1)
"Therefore you should do this."
"Therefore, you should do this."

I am wondering which sentence is correct and alternatively I'd be thankful for an explanation.

(2)
"I do not like it anyway though/although it is quite tasty."
"I do not like it anyway, though/although it is quite tasty."

(3)
"What is more/Moreover/Furthermore he is an outstanding singer."
"What is more/Moreover/Furthermore, he is an outstanding singer."

Thank you very much.