Late to the party (and I haven't finished reading the thread yet), but curious why you think your current 100Mbps connection will be inadequate with a child starting secondary.
We managed through home schooling last year with three children online (one MS Teams, two Google Classroom, all secondary), occasionally an adult working from home (VPN), online piano (Zoom), harp (Zoom), ballet (Google), church (Google), Signal calls to family, Teams calls with friends, all while also being able to keep up with news websites, occasional social media and running our own mail server on the end of an ADSL2 line (sync about 8Mbps/1Mbps, throughput around 7/1). We made two concessions. Firstly, there was no TV streaming during "working hours" (but we have a radio, an aerial for the TV and I am a demon with get_iplayer), secondly I fitted a 4G modem stick to our router as a backup and peak-balancer with a very cheap connection package, but looking at the logs this only came on very occasionally and I didn't see as much as 1GB used per month by this route.
It's the uplink speed that's the bottleneck for that sort of use, and fortunately the schools were happy to have cameras off most of the time.
People are being sold the idea that they "need" faster internet, but in reality most people would get by quite well with 10Mbps down, though something a little faster than 1Mbps up would definitely help in these days of video calls.
The caveats I'd note are:
- 4k streaming TV needs around 25Mbps (according to Netflix) (so 100Mbps could support up to 4 simultaneous streams). Note that HD streaming rarely needs more than 5Mbps
- gaming does require a fair bit (we don't do online gaming), but is far more sensitive to latency, jitter and packet loss than raw speed so a solid 10Mbps with no contention and a good ISP might actually be better for some types of games than 36Mbps or more with a poor ISP. Also, wired is always better than wireless (that is, the network in your house)
- from my own perspective, I do some downloading of large files, so faster is always better, but the alternative is patience - or leaving the thing to download overnight
The upshot is that our home internet costs (above the cost of running a landline, which we'd not be without) a grand total of about £15 per month (ADSL + 4G, varies a little according to actual use of the 4G) and I'm struggling to justify more-than-doubling that to upgrade to a 40/10 FTTC service, especially now that the children are back in school.
M.