Question: I like to work with the tex on one half of the screen and the pdf on the other. 

How do I hide the console window (with transcription log, error report, etc) unless there is an error? And how can I keep the focus on the tex window?

That way, I command-T to see my pdf, but keep typing.

Answer: 
You can find options for those in the preferences:

* TeXShop, Preferences, choose tab "Console" and set "Show Console" to "when error occurs" (default is "always")
* TeXShop, Preferences, choose tab "Typesetting" and set "After Typesetting" to "continue editing" (default is "bring preview forward")
I also encountered the bug on MacOS High Sierra (10.13) in full screen split mode. 
It might help to drag the console window away as a separate window outside. And then switch to the full window in TexShop. When you click 'Typeset', the console shows the result like in backend, and you will not get bothered by the console window.