Welcome! 
Some people like hardwired sensors, some people like battery powered ones. Some people have both depending on the specific use case for each device.
Battery powered sensors have two advantages: you can put them anywhere you want to, and a potential intruder can’t disable your barrier detection sensors just by cutting their wires.
Hardwired sensors obviously don’t have to have the batteries changed.
There are many people in the community who have added mains power for a specific individual sensor because they had a particular need for that. You can see those project reports in the community – created wiki Quick browse lists by looking in the project reports section and choosing the power management list.
I haven’t heard of anyone trying to do entire banks like you are. I think most people would just buy hardwired sensors to begin with as they are much less expensive than the battery powered ones.
In particular, you might take a look at the following project in that regard: