Guild Wars 2

Good Day to all:
I have the idea of making a good app for GW2 most for storing Builds and stuff (android app). I plan on getting data from gw2 API. and of Course ill be using Images from GW2 Art.
My question is: Android app will be free with some “paid improvements”, DO I HAVE to ask permission to ANET to use their ART ICONS or their API? do i have to pay them a % of earnings (if i have any)? I dont wanna work and then get issues with ANET (legal).
Or just to avoid all that make the app free with ADS?
Everyone can answer but i would be nice if some from ANET could send me into the correct direction to get answers.

Thanks for your time Community.