I will second the others that only suggest Signal or a variant of Signal like Langis or Molly. Everybody has each other’s phone numbers, go with Signal so people don’t need any other contact information.

For which ROM to use, I believe any ROM based on AOSP will suffice because even that will fully eliminate all Google tracking, I think LineageOS is the worst one. I do recommend Pixel since you can lock the bootloader after flashing it. You could try CalyxOS.

For privacy, I only use phone for communication, I don’t use cell data service so no internet when I’m outside, no messaging, until I connect to wi-fi again. In F-Droid I turn off all anti-features in settings, and everything I install is from F-Droid. No social media and no Aurora store to use Play Store

I have never heard of Bastyon before. I have an account on there. It would be helpful if it had a libre app to use.

Users can have upvotes and downvotes disabled in settings so they are never see how many vote up or down.