How to narrow down choices when finding a new bike?
As someone who has recently done the same thing, I'll think I can help with this. 
The biggest trap I fell into was overthinking it.

Some of this might sound a little backwards but it's my thinking at least.
As a starting point, you need to work out your budget.  No point considering anything that's outside that.
Sounds like you already have your intended use sorted, but that's a pretty big thing to nail down
Next thing I would suggest is pick an pick a bike shop that seems to know what they are talking about and not just flood you with marketing jargon.  Find out what sort of follow up service etc they have.  As a starter, you're probably going to need some help with setup &amp; maintaining the bike so pick one who will.
After that, take a couple of options from that store in your budget for a ride, see what you like.
Then buy the bike.