Hey Alex! Kinda late but if it helps.. I performed the HDD - SSD change recently in the i5 2.9 Ghz model and I didn’t need the thermal sensor. I placed a Samsung EVO 860 500GB and also upgraded the RAM to 16gb, it’s a new machine. I’ll try the PCIe Nvme SSD storage option soon, we’ll see how it goes/ if it’s worth it. I know you mentioned that you’ve opened up macs before but still, be careful. Other than that it’s not that difficult, just follow the macsales youtube tutorial and you’ll be fine. Good luck!