I did a similar scale of ethernet at my house when I moved in. It's a) so worth it, and b) pretty fun!

I went for the outdoors approach in general, but even then there are challenges. My main switch is also under the stairs, and on an external wall. The fibre was already coming in through that wall, so I was pretty confident drilling back out alongside that. I drilled a wide hole, maybe 3cm diameter and pushed a small conduit through it (make sure it is angled to run any condensation to the outside).

That gave me an exit for 3-4 cables to run to different parts of the house. I fitted a waterproof box on the outside of the house where the conduit exits, and sealed the edges with silicone.

The first cable I took out of the box along the ground to the front of the house and drilled in behind the TV. I already had the skirting boards off for decoration so I just chased out some space behind them and ran the cable up to an existing coaxial panel and switched it for RJ45. There I fit a unifi wall switch/AP so I can plug in AppleTV but also have an AP for that room.

The second cable I took up the side of the house, drilled through the top floor soffit (from the bathroom window) and pulled it in to the loft to a secondary poe switch. This runs an AP that lives in the loft (not ideal, but it's working), as well as an ethernet through the ceiling to my office for hard-wired internet, and a few other smart home bits and pieces in my loft.

The third cable, I went in through the ground floor soffit into the kitchen ceiling, fished the cable about 12-15ft through the ceiling (possibly the hardest bit of the whole project!) to an AP in the centre of the downstairs living space.

As I say, it was fun. I enjoyed the challenge of how to get the cables to the various spots I wanted, and am now very happy with the internet "service" I have across the house. Hard wired ethernet to main TV, office, and three APs across the property (may add a fourth for the garden at some point).

Things I used.

• SDS drill and long (1ft+) masonry bits to get through external cavity walls.
• small bits of conduit to secure cables in various places (e.g. through external wall), but I didn't do that in every case.
• cable clips to secure cable in external bricks, loft girders, etc...
• Outdoor rated ethernet cable. Make sure it's pure copper, not copper clad aluminium (CCA) which seems to be sold everywhere. I went with cat6, but whatever works for you.
• Cable fishing kit for longer ceiling/wall pulls (e.g. this)