SM = 2-bit MLC ("MLC"), PM = 3-bit MLC ("TLC"), 96x = 960 generation, the "1" at the end means client while "3" would be the enterprise/datacenter (20110 w/PLP) version. Samsung's NVMe driver will work for the SM961 and improve performance, but Magician will not. OEM drives and firmware tend to be less performant than their retail counterparts for various reasons, e.g. power states.
PCIe bifurcation support is dependent on the specific motherboard. I cover an accessory/adapter
here with some details on that. It's possible to get an adapter with its own bifurcation but they're very expensive ($200+). If the motherboard doesn't have hardware (PCIe switch) and software (BIOS) support you will not be able to get it to work. Even if you do, it will likely take lanes from your discrete GPU if one is present.
Depending on the motherboard you can get a (singular) M.2-to-PCIe adapter (cheap) and there are also USB enclosures, yes. I cover one
here. NVMe drives are PCIe and do not work over SATA (outside SATAe, which is expensive to convert, if you even have SATAe support, plus limited to x2).