The first three examples are incorrect. Example (a) is especially odd, as you use the past tense ("he talked") with a future time ("the coming week"). Example (b) is *almost right, though.
"Over the next week" would usually mean that something stated will gradually, or incrementally happen during that time period, for example:
We will talk about it over the coming week.
This could mean that the discussions will be ongoing throughout that period.
If you wanted to indicate that a single event will happen at some currently undecided time during that period, you would instead say:
We will talk about it sometime during coming week.
Your final example (d) is idiomatic, but it doesn't necessarily imply that you went more than once - it would be understood to mean that you visit there spanned the holiday period.