How many gu packs do I need for a 5 minute ultra? Also do I need to wear nipple tape for this ultra run too? Should I buy a hydration vest aswell?

One GU 5 minutes before, and then I would open another one at the 3 minute mark and just lick the opening -- just a taste is all you need to get through the remaining 2 minutes.

Protip: kill two birds with one stone and slather the gu on your nipples to avoid chafing and keep a tasty snack close at hand