Although some English dialects do use 'for' to indicate intention. (I'm for going to the shop to get the paper = I intend to go to the shop to get the newspaper). Or at least that's how I remember it in the Scotland of my youth.
Incorrect. "andare a" is equal to the (US) English construction "to go do something" (= to go somewhere to do something) and it has no meaning of future (expressed in the corresponding constructions in French, Spanish and Portuguese).
The current translation on 08/24/2019 (I am going to open my box) is inaccurate. A better translation is "I am about to open my box" and "to be about to" is not interchangeable with either "going to" or "will".