There are pcie adapter cards that can hold 4 m.2 drives.
That said, ANY SSD will be better than any hard drive.
Actual perceived performance differences between m.2 and 2.5" or pcie vs. sata are actuallly minimal.
The big benefit of a SSD is minimal latency, and that is similar among all of them.
Yes, pcie drives are faster in sequential benchmarks, but there is very little of that in normal operations.
There is a youtube video showing perhaps a 1 second difference in game load times.
Then, there is no difference in performance between two 1tb ssd devices and a single 2tb ssd.
If you need more storage, buy a larger ssd in the first place.