Greetings

Situation: have just moved to a new ISP - - - fiber optic direct to my
equipment so I'm finally done with the terrible speeds and worse
support on a fixed wired high speed (total misnomer) ISP.

Router is an ASUS RTN12D1 running a variant of dd-wrt 3.0.0.4.380_8120
at lan ip 192.168.1.9 .
(Really want to relegate this m/c to working only as a wireless AP!!
Have been having DNS issues sporadically over the last couple weeks.
Usually taking a router power cycle AND me to reboot my main box so
that I could have web access again (wireless access would happen
without system reboot).)
Have an i5 m/c with OPNsense installed. Its telling me that its lan ip
is 192.168.1.208.
(I cannot ping this machine from my main box. Cannot get access using
a web portal either. Need to complete the configuration of this setup
and would like this to be my new router.)
Have a NanoPiR4S (4GB version) with OpenWRT installed but not
configured. Asus router says that its lap ip is 192.168.1.1 .
(I cannot ping this machine from my main box. Cannot get access using
Luci either because I cannot complete the configuration of the
machine.)
Wife's cell phone says its connected to the network but has not web access.
(Can see the m/c on the router - its ip address is 192.168.1.228. Can
ping this m/c from my main box but the times vary considerably.)
My cell phone is connected to the network and has web access.
(Can see the m/c on the router - its ip address is 192.168.1.30. Can
ping this m/c from my main box and the times vary considerably (not as
much as previous cell phone but her's is also further from the
router.)
I only have one option for internet access so when I shut down the
asus router - - - no web - - - so I can't troubleshoot or access
configuration recipes.

So - - - - am I having all these issues because I have a number of
router class m/cs running all at the same time?
Is the asus router getting flakey?
(Is some software being stretched too far (dd-wrt)?)
These issues are about driving be crackers - - - - please anyone out
there with experience and ideas (besides cables not being plugged in -
- - tried that too).

TIA

(Almost thinking of writing TL;DR at the beginning!!)