Well, the whole equation is going through the link function, so you’re not really using a Normal prior – only on the transformed space of the parameters, but not on the outcome space.
I know, it’s confusing. Don’t worry, it’s gonna click with time and repetition. I’d actually recommend starting with simple linear regression – your use-case is already intermediate, because there are more moving parts in a generalized regression.
I’d suggest taking a look at our Intro course – we designed it to get you from beginner to practitioner as fast and practically as possible.
Yeah, sometimes… but some other times it’s gonna be the contrary 
In the end, the number of regressors is just an emerging phenomenon of how you scientifically think and justify your model (what we call the “data generating process” in the Bayesian world).
Definitely. These concepts are super important, and often forgotten by beginners. That’s also why we insist on them in the Intro Course