Let me just say I've never added fruit to beer. I know many people do. It does seem like an interesting idea.
However, adding mangoes to your beer will add sugar and will probably lead to a rejuvenated fermentation. If you add the citra and cascade when you add the mangoes, you will lose a lot of the benefits of the these hops.
If you really want to use the mangoes, add them, let the yeast work for a couple days, rack into a secondary, then add the citra and cascade for a week. Be aware, you will not get any sweetness from the mangoes because the yeast will eat the sugars.
However, if you want just the sweet mango aroma, then just dry hop with galaxy hops and maybe some citra too. I find that galaxy really gives my IPAsa a nice mango aroma. Don't use the mangoes at all.
As I said, I've never used fruit in my beer, so I'd stick with just using the galaxy hops. Either way, you'll probably get a tasty brew.