He also changed the locks few months ago, which is also not allowed.

I’m looking for recommendations on lock sets for my common area entry doors on my 4 plex.

LOI's doesn't lock you into a contract until all requirement/contingencies are satisfied.

What about the ground up developer that exhausted their interest reserve because  the construction debt was tied to the fed rate, but the project is still perfoming well and they want to hold off on refinancing a bit longer because its still a great long term hold but given the pre-payment penalties they are opting not to lock into a perm rate yet beleiving favorable financing will be available with a patient approach.....

It's good to note as well that you're not "locked in" from using one or the other, just simply how the activity was during the year.I will also state that you don't get a choice in the matter for how it's reported for 2023.

Over the years, I have built local teams ( agents, contractors, property management, inspectors) that serve as my eyes and ears. 

I also like the battery powered lock boxes with a hard key option (just in case)

It may still be useful, depending on your situation.If it is locked, then qualifying for material participation in 2025 will not unlock this loss.

Cameras, security guard, locks, types of lights?

Completely lock/key separate and 0% owner personal use.