advice material for hydraulic flange

[Kaminari]

Good morning to all,
I'm asking for advice. Summary: in my apartment I found myself, in the bathroom, an old unused monocommand mixer that bothers the placement of some furniture. as I don't want to split wall etc to remove everything I'm thinking of removing the tap cartridge so that I don't have the "outside wall" footprint anymore. to do so I am drawing a blind flange that goes to copy the usual 3 holes of ceramic cartridges with seats for or.
in the first line I was thinking about the inocx 304 but could there be the problem of the galvanic currents, better to go on copper or brass according to you? or even go on a rigid plastic like pe? using one of the many sites of "cnc online" the material choice will not be very vast. . .

Thank you!

 

[TETRASTORE]

As the hydraulic system of the house you should not have a water pressure greater than 4 bars, I would exclude plastic materials if in contact with hot water (of course it depends on temperature and thickness) but to have greater seal guarantees I would turn on the brass (by bar), easy to work, resistant to corrosion and easily available at online cncs.