Can we install an M.2 Internal 525GB SSD as the boot drive in this laptop?
It has a free M.2 slot, yes.
However this laptop has a very poor quality display, and as such I would advise against it. The contrast and viewing angles are terrible. Getting performance that fits your needs is important, however the difference between a good quality display and a not-so-good one is in my opinion one of the absolute most noticeable spec-based differences. At the price Dell is selling this laptop, there are plenty of options with similar performance and decent displays at the same time.
The 1920x1080 model display is low quality, the 4K 3840x2160 model is fantastic but costs more.
Check out reddit.com/.../ for recommendations on what to buy.
Inspiron 7567 versus good display: