Hi,
Disable the “auto” option and move the buffer size slider to 1024. Then it should work.
No, I am sorry. There is no manual available.
In VST Transit Join there is a button (record sync) in the transport toolbar, a brown one, next to the the metronome button. This one should be enabled if you want to record. Transit Join is then in sync with the host. That means : if you hit the record button in Bitwig, the record state in Transit will be activated, too.
For Bitwig : You managed to route the audio you want to record to Transit? You need to add a Bitwig Audio Recorder module before the Transit Join module, choose the audio source and there you are. Yes?
And of course. Transit supports drag and drop. I.e., you can move clips from a host to the Join editor. Or a file from the Explorer/Finder to the Join Editor. But Bitwig does not support to drag clips to the Join Editor or any other VSTi editor 
But you could export your audio stuff to your Explorer and then drag it to Join.
Maybe I can talk to the Bitwig development team about that missing puzzle.
See you,
Michael.