The amount of total hops used depends on your batch size, OG, and intensity of aroma desired. IIPAs like Pliny and Heady may use upwards of 4-6 oz. for a multistage dryhop. But I wouldn't recommend adding this amount to 3 gallons of a 1.055 OG IPA in one stage.
For a 5 gallon batch of standard IPA, 7-10 oz. total hops is good. Figure 0.50 to 0.75 oz. dryhops per gallon of beer. Bump the rate up slightly higher (from 0.75 to 1.25 oz. dryhops per gallon of beer) if brewing an IIPA.
OP, use 1 oz. of the Palisade in the dryhop as well as your current plan. Palisade is fruity which will help your goal. Citra is even fruitier. I would do a simple 60/30/0/DH schedule (30 min is for rounded bitterness) with the majority of the total recipe hops at 0 and DH. Focusing on 0 & DH will give you a hop flavor and aroma profile that is through the roof!
How are you adding/preparing the mangoes? Fresh, frozen, puree? Any special treatments before using?