Setting up HomeNet with multiple routers

In another post my install/configuration of OpenWRT 19.07.3 on ER-x is described.

Networking is not a subject I understand very deeply. Especially the IPv6 side of things. However, it seems important to understand more than I do now. Any help is appreciated.

All connections are wired Ethernet. End nodes are various devices including iOS and Linux clients. Once I connect a second router downstream from the first there seem to be automatic changes that create connectivity issues.

To start with, I would like to be able to send print jobs from a Linux machine downstream from the 2nd router to a printer that is connected to the 1st router.

I believe that is a firewall configuration issue, but would appreciate a hint of how to configure or where to look.

you only want 1 router in a system so if you are using the 2nd router as a switch / access point
then only configure it as such look at "dump access point" you don't want it to do any NAT routing

Thank you.

I was planning to use the second router with a VPN service in order to provide that to devices downstream. That hasn't worked very well yet either. My ignorance is apparently much deeper than I first realized.

The purpose of using OpenWRT on my gateway router was to a better ability to configure with security in mind.

The whole IPv6 topic was not in my original thinking. I see other persons asking questions about how to disable it. I was trying to go along and keep ipv6 by using HomeNet for a better configuration than I would know how to do on my own.

At this point, with Homenet appearing to be an orphan project, maybe I'd be better off just rolling back to IPv4 only on gateway router to start.