It depends. What I would do if you are interested is buy a cheap damaged phone that is still usable and then flash it with Lineage. From there you can break things without causing issues on your main device.

you should be able to import/export contacts to a file, on most systems i think. also check if theyre stored on the SIM card itself, or in your phone.

I LOVE GRAPHENEOS

There are 2 apps I use that won't work on graphine. I've been trying on my second phone and I can't make it work.