Shouldn't be anything to worry about, remember the m.2 slots are on the other side of the motherboard anyway so they don't contribute directly to the temperature inside the main chassis. I wouldn't put anything super high performance in there though (like a FireCuda 530) and anyway I think for most purposes even a PCIe 3.0 NVME should be just fine. I have both m.2 slots used in my P350s - the 256GB PCIe 4.0 NVME it came with and a PCIe 3.0 1TB drive (2x Corsair MP510s, 1x Crucial P2, 1x Sabrent Rocket) and it doesn't get particularly hot as far as I can tell (fan is silent).Oh what are those random brands and does increase in size results into more heat I was thinking to install 1tb but not sure sata, nvme gen 3 or nvme gen 4
If you intend to use ESXi at any point in the future, though, note that it's pretty cranky about consumer NVMe drives (there are some notes in the original post in the ESXi section).