My perception may be biased, but I'd say it's quite common to have 10/10 Mb/s connection included in the rent and many opt to upgrade it to 100/10 for 10-20 euros a month (roughly 12-24 usd)

Many vendors make routers which have 4G modem which then send out a WiFi signal + have Ethernet ports.

In rural areas the ADSL prices started climbing up a few years ago and most moved to cellular (60 euros for 21Mbps ADSL vs 25 euros for 50Mbps 4G). As of recent fiber connections are getting good in rural areas as well, so people are switching to fiber (40 euros for 100/100Mbps, 60 euros for 1000/1000Mbps). People who have both 4G router + fiber are quite rare.

In my experience some channels on 4G are quite ossified and during peak times you might even get a better throughput on 3G.

Almost everyone I know from Finland has home broadband as well. Mostly due to home computers and less than ideal indoor cell service.

There was some switch to 4G for home internet (with mifi/usb dongles) as well, mostly due to aggressive pricing some years back. It was a good alternative to ADSL and cheaper, but became congested once a lot of people started using it. Yet, fiber is much more ubiquitous these days and is much faster and cheaper than either of those.

I don’t know the answer to your question, but back when I had unlimited tethering with fast 4G, I would basically just have it on all the time to use my laptop on the go and treated it like home WiFi. So even though I would have home WiFi and be connected while at home, I would still rack up 10+GB of usage monthly. That is to say, I can imagine hitting 17GB could be common every month even with home WiFi depending on the culture of usage.