debian+phosh running on PinePhone

[a-wai]

1) apt-get install openssh-server
2) systemctl enable ssh
5) can Vim be installed by default ?

openssh and vim are included in the pinephone-devtools package, I believe it is a reasonable compromise rather than having it installed by default, which might be a security risk, as mentioned by others.

6) one of my aims is to use Jami with pinephone
- it doesn't scale properly at all (even when changing scale in /usr/share/phosh/rootston.ini, can we fix it or do I need to fire up issue in Jami's git ?
- the keyboard with Jami is not working properly. All of the keys do nothing, I have noticed that pressing backspace key it outputs '=' meaning that I cannot login at all, again can we fix it or do I need to fire up issue in Jami's git ?

These look like issues related to Jami being X11-only (but I might be wrong).
As a general rule, issues with third-party apps (even the default ones) should be reported upstream, as I'm only putting things together and focusing on having as many hardware features working smoothly as possible, which is already quite a lot to do with very little time.

7) (again) can we have another keyboard ? the one there currently is not really usable e.g when working in terminal. I've seen better, not sure if in UBports or pmOS/plasma

I don't think so, squeekboard is (to the best of my knowledge) the most usable mobile-friendly wayland OSK so far. It is clearly far from perfect, but I actually find the terminal layout quite usable, have you used this layout ?

8) browser - FF works, but I really hate the zoom in/out.
- yes I know it's FF's fault, but is there any alternative to FF which is mobile friendly without sacrificing usability/security at all/too much ?

Epiphany ("Web") is also installed by default, you can give it a try.