Help with Video Doorbell Pro 2 install with Nutone IM-3303

I am attempting to install a Ring Video Doorbell Pro 2 (2021 release, purchased new last black Friday). Our home has a built-in Nutone IM-3303 whole house intercom system (from previous owner, assume installed decades ago). This consists of the base station, 4 intercoms in bedrooms and a doorbell unit.  I've uninstalled the doorbell and installed the Ring, connecting the two wires that were connected to the Nutone doorbell button to the Ring (and leaving the two that were connected to the speaker clipped and unconnected).  The Ring does not fully power up such that it can be configured, but does power cycle every (roughly) 30 minutes, so clearly is receiving some current.  I have not installed the Pro Power Kit as there is no dedicated Nutone chime unit. Figuring out if / how / where to install this would seemingly help my cause.  I have located a transformer in the garage wall (close to the doorbell). It is labeled a Nutone Scoville 105-N 15VA 16V.  I'd love any guidance on how I might solve this, or, how to address with an electrician such that a (guessing) $150 labor + $20 part effort doesn't magically inflate to 10x that (seems to happen frequently here in San Diego). Importantly: I have separately purchased a Ring Chime / do not care about leveraging the Nutone in any capacity going forward.  Thank you!