I was at that point as well and basically followed @R2D2 's steps here. As I also wanted to add Magisk, so I created my own notes, which are mostly similar and only a bit different at the Magisk part. So I did not post it again and just confirmed that it worked. (maybe helpful for others when we add another wiki post like “Howto install Calyx OS with Magisk on FP4” or so)
Or you just combine the infos of:
like I did. 
(and I didn’t though about the patch-level thing, but I directly flashed Calyx after my FP4 was delivered)