Imo white backsplash, white grout. Subway would work but it does not have to be subway. You have a lot going on already, the backsplash shouldn't be a feature.
Heres my kitchen which also used original exterior brick (a chimney in my case) that was not in perfect shape. I used a white backsplash, so (imo) it's subtle and neutral but its not the ubiquitous subway tile although that certainly could have worked too.
https://www.houzz.com/discussions/pittsburgh-kitchen-mudroom-closet-addition-reveal-dsvw-vd~4948003?n=40
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This one is really pretty in the blue color. But dang, it's expensive!
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