"Teacher Wang only wants a cup of coffee."
Hello. 王老师只想一杯咖啡, in Chinese, means "Mr / Teacher Wang only thinks a cup of coffee."
As you might have noticed, this sentence doesn't sound right or natural in English. It doesn't sound right or natural in Chinese, either.
When you use 想 in a Chinese sentence to express one's desire and wishes, it is almost always followed by a verb. For example:
想做 = Want to do
想吃 = Want to eat
想喝 = Want to drink
By this logic, 想 appears to mean "want." But that is not the case. It only means "want" when another verb immediately follows it.
想, by it self, always means "think." For example:
想事情 = Think about something / things
想答案 = Think about solutions / answers
想点子 = Think about ideas
There, though unnatural and would probably never be said by a Chinese, the most accurate translation of your answer, 王老师只想一杯咖啡, would be:
"Mr. / Teacher Wang only thinks about a cup of coffee."
Once again, I must emphasize the fact that this sentence does not make sense in Chinese.