Also, just so you are aware... you wouldn't have to drill holes or run wires anyway. Not this day and age.
I installed my 20P system well after my house was built. All wireless sensors. In 5 years, I have not replaced one battery. I've replaced a couple sensors that went bad, but no dead batteries yet. I probably have 20 or more sensors too. The wired sensors are better for sure, but every year that goes by, that because less of an issue.
Regardless of that, I would still try and use what you have like you are doing. Keep in mind that programing a Vista system like that from scratch is not easy. Those systems are meant to be installed by the "pros". I was able to do it though, and I'm nothing special. Lots of manual reading, and YouTube videos.