OLU

you can go into bios and set cpu voltage to 1.2v, if it would boot, try to set it even lower by little bit every time, if it won't, try to increase it till it boots.
for hard ware, i would definately change the fan, if you dont want to void ur warranty, buy an external usb case fan like what i did

Double check in the bios you might be able to disable some cores on the cpu. Unfortunately that is the only way I see you being able to reduce running wattage without changing hardware. Maybe try running the PC with the PSU outside of the case and see if the problem continues. If it continues then there is something wrong with the PSU or something else is wrong with the system.

Technically, same issue. The harddrive being external will have its own latency issues + the throughput issues of USB. I would scrap the optane drive. I understand their value, but if its costing you a valuable m.2 slot for an nvme SSD, its causing your more harm than good. A little optane acceleration of a HDD is much worse than a full 1 TB+ nvme SSD. Optane's true "calling" is to accelerate harddives in very economical PC's, or be used in the server space for ZFS caching and such.

I would remove the Optane "system" drive and replace it with an nvme ssd.
 
Technically yes, USB 3 is fast enough, but it isn't set up the same as SATA or nvme is. It can't handle nearly the IOPS that SATA or PCIe nvme can, so for big file transfers USB 3 is "plenty fast" but for program access where its always reading and writing little things all the time, it wouldn't be great. It would work, but I would 100% do my first solution before doing this.

it's a macbook pro, haven't find an adapter yet

this is 275CAD when i switch it to canadian walmart, which is about 60CAD more expansive than the MSI one with wifi.