@Arnoldko
About your question:
UBports is a German foundation. And when I search for "public transport" at open-store.io (app store for Ubuntu Touch (UT)) I see four German, two Spanish, one Norwegian, one American, one Hungarian and one Swiss app(s). So you have maybe slightly more people who know some things about UT in this countries, but I do not think that this is significant.
It probably depends more on what you want to do and how you want to structure your company (How closely do HW and SW teams need to work together? Where is the head of your company? Is this a commercial project?...).
If your hardware team also takes care of firmware and drivers and you are only searching for some people who write some apps for you, you should find people who can do some C++, Qt and server stuff nearly everywhere.
Specifically for Ubuntu Touch, you could maybe post a job description in this forum and let the people work from home.
Some time ago some people related to Volla did a fundraiser to bring Android apps to UT. They commissioned some Russian developer and it was very successful. So maybe this could also be an option for you:
https://forums.ubports.com/topic/5907/open-ubuntu-touch-to-all-android-applications/
https://forums.ubports.com/user/stanwood
https://www.gofundme.com/f/anbox-on-ut?utm_medium=copy_link&utm_source=customer&utm_campaign=p_lico+share-sheet
About no phone numbers:
A lot of messengers and other services depend on verification via SMS. This is maybe something you want to consider.
About using UT as a base:
Please be aware that Ubuntu Touch has some limitations and depending on what you want to do (how much you want to modify the system), it could maybe be more convenient to start with something else (like Debian). There are currently also some people working on Lomiri (the desktop environment of Ubuntu Touch) for Debian.
But this very much depends on what you want to do.
