> The 'radio', as it called by my isp is outside about 45 m away on a
> tall roof with a
> 3 m mast on it with the radio on the mast. The ethernet cable runs
> from that 'radio'
> to the house where there is a little box (with plugs to provide power
> to the 'radio')

That is probably a power over Ethernet, PoE, injector. It puts power
in the Ethernet cable to power whatever is on the mast.

> all of which I have zero control over. The first piece after this
> little box (and its about 3 cm x 5 cm x 12cm outside so its quite
> small) is my router and and and.

So this first box of yours should be the center of your world:

It gets its WAN IP address using a DHCP client on the WAN port,
connecting to the radio up the mast.

It does NAT out the 'WAN' port.

It runs a DHCP server, giving out IP addresses to all you devices.  It
is a good idea to give each of your devices a fixed IP address.

It does DNS for everything in your home network. It can relay requests
to your ISP, or to But ideally you want it to answer when
somebody ask about server.home, ipad.home, laptop.home, or whatever
you call your devices.  What you don't want is the devices in your
house directly using the DNS servers of your ISP. If your ISP falls
over, it does not matter if you cannot resolve names on the internet,
but you do want names for your own devices to keep working. So they
need a use a local DNS server which is still running.

In my case, i have a WiFi access point doing all this, running a
recent OpenWRT image. It could be for your use case, the typical 4
Ethernet interfaces of a WiFi access point are not enough. But you can
expand that by daisy chaining any old dumb Ethernet switch with more
ports. Its this first box that does all the real work.

It is not a black art, but it is something most people never need. All
their devices are just clients connecting to servers on the
Internet. But when you have your own NAS box, Linux desktop, media
server connected to a TV, lots of embedded devices in the cellar which
you are kernel hacking on, VPN connection to the mother-in-laws home
for off site backup, etc, you quickly need more than just clients
connecting to the Internet.