Apologies for late reply.
So I had set the cpu governor but after the upgrades I noticed that it got reverted to default (full range 400Mhz - 1.8Ghz, for helios64). It has been surprisingly stable with bookworm, no instability issues or kernel panics really at all!
I got mergerfs + snapraid running through the CLI and have my share exported over samba and nfs. So far so good!
I was still a little bit concerned about a kernel upgrade borking the whole thing given past experience and after the system was up to date I froze the kernel upgrades in armbian-config, I can unfreeze later but just to be safe in the short term idk.
I installed docker via softy and have loaded up a few containers and reading storage from the attached ssd m.2 drive on the mobo, all seems good there!
I ran jellyfin and disabling transcoding and only using direct streaming, didn't have a huge impact on the system it seemed which is perfect! When it downloaded media files it definitely kicked the CPU load a bit over 4.0 (4 cores, so over 4 is high right?). There was a weird error where the contianer crashed during this and I thought it had kernel panicked but it was something to do with the container, i am not sure -- docker normally does not spit out an error message to console as it did for that. I am not using swarm mode on the helios but you can set a cpu limit under a deploy setting in compose and run it with a --compatibility flag which will translate it. I set the limit to 1.0 (thinking 25% max cpu capacity in my head, i am not sure how this works out tbh). It works pretty well to keep container constrained and not overwhelm the rk3399. I would like to take advantage of the gpu but apparently there are issues with ffmpeg and rockchip cpus for hardware encoding and other features? Looking into this more.
So it seems my only issue at the moment is the eMMC boot thing which i am kind of at a catch 22 for...