@OP,
Looks like you will have a fantastic Christmas Market adventure. We did one back in 2014.
The gears you have and described will be fine. I concur that bringing less is better than more. Having said that. Here are my experiences shooting Christmas markets.
1. Purpose of your photos. For print or for social media?
2. Resolution wise, anything over 12 MPX will be fine for printed coffee table book to sharing in social media.
3. Major concern is NOISE (i.e. low light performance) and control of Highlight & Shadow. This concern supports the notion of shooting in RAW format, that allows some simple post edit. Later models of iPhone should have RAW capability, I think. I use Samsung Phone so don't know about iPhone.

Below are few examples of what I said. They are from my trip in 2014 what I shot with Nikon D90 (12.4 MPX) in RAW (NEF) format.


















I maintain a "private" Travel-Photo-Adventure web site, happy to share my Travel Journal on a Christmas Markets trip with you, use link below;

Christkindlmarkts - stefano PHOTOGRAPHY (smugmug.com)