For a 4mo old, i might suggest a different stroller other than a jogger. I would imagine your 4mo is going to sleep a lot and like to lay on a flat surface. When our peep was 7mo, we had a stroller that could sit up or lay flat. The canopy would shade from sun while leaving both ends opens to allow for cross ventilation.
The biggest thing we found was to seek indoors and shady areas whenever possible, hydrate, hydrate, hydrate and keep him dry. Changes were frequent. We also would lay cotton towels on teh cushion of hte stroller and change them out a few times a day to keep the stroller dry.
Personally, I would stay away from mister fan on teh baby. If using a regular type fan, i would not put the breezed directly on the baby. It would be too easy to give the baby a chill when in a shady area or in a place with AC. Disney tends to blast the AC pretty hard in the summer months.