Great to see the final specs and due to be released on Q4 this year! I've found my Nexus 5 replacement
When the Pinephone/Librem 5 phones are released. Will UBports consider them flagship-type models due to their openness and will development be focused on those devices? If so will this mean older models like the BQ E5 and E4.5 become unsupported?
Regarding Posteo, i'm not familiar with it nor the calendar so I'll let someone else reply to you.
Dash etc: You can download Ubutnu Touch Tweak Tool (UTTT) from the open store and mess around with all kinds of settings etc. with that app.
Anbox: Anbox is still being worked on although there are some more important issues being address first so Anbox is not the primary focus.
Roadmap: There was one but I think they felt it was giving false hope to people that saw it if the features on there were not implemented in time so it was removed, I think you will now only get a next OTA milestone.
Keyboard There are some settings in the system settings for keyboard but nothing about enlarging the space bar as far as I know.
I can't help you with your problem but are you on Telegram? If so you can join the welcome channel and get good help there, if you don't manage to get help here (not everyone reads the forums regularly).