Rooted devices never get any OTA updates, only manual. With open BL no OTA.
So if you upgrade to A12 via Odin and install TWRP, you have to wipe data partition anyway to decrypt it.
No reason to root A11 before, when you start from the scratch anyway. So backup everthing you need.
Restoring your apps on A12 will get you problems sometimes. For me, A11 worked a litttle bit better, but you'll get no security updates in the future.
My phone is 100% virgin with only the BL unlocked (no accounts, no app or system updates.) From here ... what would you do to get to A12 + rooted - with the least work or complication? I'm good with either TWRP or no TWRP.