When you see the word heptahydrate, what number should be written in front of the formula for water? 5 6 7 8?

Hept for 7, hence the number is seven.

If the water vapor content stays the same and the temperature drops, then the relative humidity increases. its vise versa.if the water vapor content stats the same and the temperature rises, the relative humidity decreases. so, yes, i'd say that temperature and humidity have a strong relationship.