A teacher is wonder source of challenges and valuable critique and evaluation of your music progress, not that TBers aren't.
Serious students of bass/music get a teacher. Why? same reason Roger Federer or Tiger Woods had/has coaching. It provides a perspective you can not get yourself. It cuts the learning curve exponentially and keeps you practicing.
As far as good study of all the keys, the classical bass Method Simandl book 1, goes through every key in logical progression. It will teach you good fingerings for upright, some logical use of the third finger can easily be interjected for use with Bass Guitar. It will also teach you position shifting. If you can play this book from start to finish, you will be able to play the bass and have a good solid foundation in theory and fingering and probably be a good sight reader too. FWIW