After much search and research and a little luck, I figured out the answers to my questions, plus a further clue. For others who encounter these problem:
First Solved Problem, Seeing all MariaDB databases:
This appears to be normal with MariaDB, when first linking to the database. When, instead, I come in by double-clicking on the Register database, I see what I want: only the current, appropriate database.
Second Solved Problem, Tables are read-only:
Tables created using MariaDB and terminal window are read-only. However, tables created within Base are fully enabled.
Further hint:
I was unable to open the database by double-clicking on the Registered Name in my file manager. I found that I’d created a different username in the CREATE statement in MariaDB than the one I was using for username logon in Ubuntu. ReCREATEing the username in MariaDB fixed that problem.
Now to do some real work!