Running 2 UTM firewalls in parallel

I am after some technical advice from the brains trust…
Basically, I need to know if it is possible to run 2 UTM firewalls in parallel.

I am currently upgrading my entire home environment, which will include replacing the existing UTM with a newer machine and a clean install.
I am also replacing my current server environment with something that is more current and actually supported by Microsoft.

Over the years I have not been very diligent in cleaning up the UTM when entries have become redundant. I figure it will be simpler to just start from scratch, adding only the settings that I require now.
Sounds simple, but as most would know, it’s probably going to be somewhat more involved than that.

As much as I only have a home environment, my configuration is not what would likely be expected, as I run a Windows domain that includes an Exchange mail server and I also have my own web server. A throwback from working as an IT contractor for over a decade. Sadly, that was over a decade ago, so my brain is hurting trying to get up to speed on current server technologies.

There are currently 4 interfaces configured on the UTM: External, Internal, DMZ and VOIP.

Some things I can obviously do in a lab style network setup, like setting up the AD integration with the UTM, but other things like testing my mail server or phone connectivity could be a challenge, if not impossible to do.

My modem is in bridge mode, so all of the authentication to the ISP is done by the UTM, which is also where my static IP address is defined.
If it helps, I can add another interface to the UTM.

Any advice would be appreciated.