I've read the section on asking questions:
http://www.turkishclass.com/grammar_questionSentences.htm
but it doesn't seem to address the yes-no question of "would you like?"

kahve seviyorsun
"You like coffee"

kahve seviyorsun mı
"Do you like coffee?"

Would you ask the question "would you like a coffee" simply by adding bir to the sentence?
bir kahve seviyorsun mı
or do you need to use a different verb to ask this sort of question?

I am just guessing, please correct me if I am wrong too ...

I think it is
Would you like coffee? -- "kahve istermisin?"
I would like coffee -- " Ben kahve istiyorum ""

When you ask someone "would you like a coffee?", doesn't it mean that "do you want a coffee". It's just the polite form. Bu in Turkish, you can't make it by using "sevmek".
You like coffee. Kahve seviyorsun.
Do you like coffee? Kahve seviyor musun(uz)? or Kahve sever misin(iz)?
But,
would you like a coffee?
(Bir) Kahve ister misiniz? (with or without "bir", both could be)
It's enough polite for most cases, but you can be more polite, by saying
"Kahve ister miydiniz?"

or you can put "acaba" (I wonder). It also adds politeness.
"Kahve ister misiniz acaba?"
"Kahve ister miydiniz acaba?"

For your friends,children and close people:
Kahve ister misin?

To say is it demek or söylemek.Thank you