Best recommendation is to max out your memory first.

This 16GB module is what I have in my 920+, and it works great:
https://smile.amazon.com/gp/product/B07F6N8L3S

If you still want to go m.2 cache upgrade, I went with this:
https://smile.amazon.com/gp/product/B08DK2FB7G

If you do add cache, I recommend you under-provision it (don't format the entire drive for use, just a portion of it), and use it in read-only cache mode.

I got this one on Black Friday: https://www.amazon.com/gp/product/B08DK2FB7G/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 ... 500GB for shared files across Windows and Linux.

The SanDisk and Samsung will get about the same read speed at like 90ish MB/s. The SanDisk is a better value storage wise but the write speed will be super slow at like 30sih MB/s verses the Samsung's 80 write.

I'd get the Samsung one if writing a lot / fast matters or the SanDisk 1TB if you mainly just writing once and leaving it there.

For the SSD you'd want something with DRAM and TLC if you are replacing your main drive but honestly HMB SSD is fine too for most. Secondary SSD that's QLC and HMB is fine. SSD power efficiency also matters and SK Hynix P31 has the least power consumption so it's great for laptops.