Getting (a little more) started

[Colin Helliwell <colin helliwell ln-systems com>]

I've got NM installed n running on my embedded system. I can 'nmcli conn up modem' and the ppp link on my GSM 
modem comes up nicely - ifconfig reports inet and P-t-P addresses, and I seem able to ping/traceroute through 
it to the interweb, but I may have some clutter.

Being embedded and headless I don't have nice GUI widgets to help me, so I might need some more manual 
configuration or tidying of stuff. 
I'm using systemd, and also have running /lib/systemd/systemd-networkd, /lib/systemd/systemd-resolved, 
/usr/bin/dnsmasq, /sbin/dhclient. 
I built NM with '--with-resolvconf=yes', and the [Yocto] image also has the resolveconf package included, but 
I'm unclear how these relate to "/lib/systemd/systemd-resolved" and whether they have common/conflicting 
configurations.
I *haven't* yet deleted /etc/ppp/ip-up & /etc/ppp/ip-down (past info from Dan suggested there could be a risk 
of conflict here with what ppp tries to do vs. NM actions).

I guess, put another way, is there something of a 'basic building blocks' info that I can follow to gradually 
build up a working but minimal/un-cluttered system, and good ways to sanity-check that things are correctly 
configuring...?

Thanks