What OS to choose for my PinePhone ?

[PhiletJosie]

I never had a smartphone, neither a mobile phone, and I'm eagerly waiting for the pinephone.
I do not know clearly what OS I should use. Here are my needs:
 - properly working phone and SMS
- easy synchronisation of contacts, agenda and bookmarks with my Ubuntu computers
- a map application with the ability to load maps for offline use, for weeks long mountain walks
- a good web browser, ideally Firefox, as it is my default browser and I already synchronise bookmarks with it
- ability to take photos

I'm thinking of using UBport, but I do not know if it will answer all my needs. And what about Pure OS, made by Purism ? Will it be possible to install it in the PinePhone ?

Thanks for any help.