Ethernet uses a star topology, so you need a switch.
Most router/modems from internet providers provide something like a 4-port switch. Many of them are garbage (ie, not gigabit, or gigabit but slow) and they stop working when the modem has a bad day.
When that happens, if you have a separate switch, you only lose internet, but the LAN still works. If you don't have a separate switch, then the LAN stops working completely.
So basically, you need a switch. There are some good cheap ones that don't use much power. Since it will be on permanently, considering its power use is important for your electricity bill. Some switches shut down unused ports to save power.
Next, you need a NAS. It should be low-power, with gigabit ethernet and RAID. It can be a linux PC or a stand-alone NAS box, although many of these boxes are slow. It must be placed in a location where it won't be stolen. Not in the basement if you live in a flood-prone area. If you don't have a NAS, then you're probably not doing backups, which means you have no data. It should be backed up manually to a SSD stored in the garden shed, and automatically to cloud storage.
Next, use conduit. Plastic conduit is very cheap. Use the bigger ones that can fit two or three Cat6 cables. That way, when you get a TV that needs Ethernet, and a game console that needs Ethernet, or an AV receiver that needs ethernet, or a living room PC that needs ethernet, you don't end up with yet another switch below the TV, just pull another cable through the conduit.
Likewise, if you do some development you may end up with two computers in your home office. It's nice to pull another cable, and not have yet another switch sitting there burning power. And then you get a printer that needs ethernet... you get the idea.
WiFi from ISP routers tend to suck. The most annoying feature is that it turns off when the router has a bad day or loses connection to the ISP. So if you use WiFi a lot for laptops, consider hanging a Netgear on the wall somewhere. That also needs Ethernet.
What devices would be needed besides a router so that the network layout would be wise?
8 port switch and NAS.
Would the use of a matrix switcher (one permanently installed in the wall)
Waste of money, just pull the cables through the conduits and crimp jacks on the ends wherever the switch is.
That's only useful if you want to switch some of the RJ45 sockets between phone and LAN, but everyone has cellphones now, so why do that?
Which categories of ethernet cable would make sense?
The cheapest you can get that will run gigabit, ie Cat5e or better. The cheapest will usually be the one that's being produced in highest quantity, so it is possible you find Cat6 cheaper than Cat5e.
Now, conduit is cheap, so make sure you run some extra. Who knows, you might get some solar panels (the inverter needs ethernet) or IP cameras for security, or...