Which of the following is the correct way?
- Date and venue is the top priority.
- Date and venue are the top priority.
If you consider date and venue to be one thing, then the first sentence is correct. Else, if the two are taken separately, then you can use are. However, if you use are, Date and venue are the top priorities would be better (rather, correct).
The point of the sentence is, I'd say, is naming "the top priority". Therefore you'd parse it as "X is the top priority", where X is "Date and venue". If you're explicitly speaking about multiple entities -- "Bob and Fred are the top students" -- then "are" would be appropriate; but since "Date and venue" is being discussed as a single entity (i.e., the space-time coordinates of an event) I'd say only "is" is appropriate.