I've been using openWrt for a few years and I've found answers to most of my network problems with the os.
I'm trying to solve this current issue of using miniupnpd in a multi-wan setup. mwan3 is installed and setup correctly.
I know miniupnpd is tied to only one wan connection, but I wondered if I can create a daemon for another instance of miniupnpd tied to the second wan connection?
Is this possible? What trouble may I stumble across if I did this?
UPnP itself is a bad idea, imagine having it run on 2 interfaces...
Jokes aside, there are many things that should align in order to make that work, so it is better to set everything manually rather than let automation to try and do its magic.
The amount of devices you have doesn't mean that all of them need a vast amount of ports forwarded. Furthermore it is a one time thing. Anyway, you have been informed of the caveats using upnp, do as you see fit.