ddh

Sure, OpenWRT is good and there’s an Adguard Home plugin for it. You don’t need to buy any hardware to use Pihole though, many people run it in a container on an existing machine. So it comes down to the functionality you need or want and the software you prefer, right?

Use the second option of a static MAC to IP map and add the relevant records to each pihole’s local DNS.

Router may not have a function you want.

You can just run two DHCP servers. Give them non-overlapping ranges or give them the same MAC to IP mapping.

If you do that, Docker is stuck on that host. If it’s in an LXC it can move to another host. Plus, backing up and snapshotting are easier IMO.

GnuCash will do the sort of security trade accounting you’re talking about. I don’t know how GnuCash compares to the other offerings, but it can be fully offline and has a lot of features.