Turns out I had some time today. Yes the staggered spinup is possible on _all_ SATA ports:

The motherboard also supports a PWM fan as the CPU fan:

Also the position of the NVME storage next to the CPU fan is much better for the heat:
1st picture is just after boot-up:

Second one is after a while when the CPU fan has had a chance to cool the NVME drive (airflow does not reach the sata controller, as you can see).
That SATA Controller is just _nuts_ in terms of the heat it puts out. I would almost put a fan on that, just to help it along.
You can quite obviously see the heat generated by the 2.5Gbit network controller, even if only running at 1Gbit.. The network cable is plugged into the one on the left. (obviously) The heat 'bleed' is also quite interesting. I would seriously consider getting a 120mm PWM noctua fan over the top of the SATA chip, the NVME drives, CPU and the network controllers and connecting it to the CPU header. And then just letting it run _really_ slowly.
Just trying find the power consumption of the JMB585 controller, and it seems it uses ~2.2W when idling, which is pretty 'nuts' compared to the rest of the components (10W total load with 2.2W just the SATA controller).
https://www.reddit.com/r/HomeServer/comments/pus673