I don't have an IOT house, so I don't know how well they'll cope. That said, most IOT chips (eg. the famed ESP8266 and most variants of its successor, ESP32) seem to only support 802.11n, a standard from 2009. Therefore any benefits are probably not going to be gained by upgrading to an 802.11ac router. Newer routers might have beefier cpu/ram, but IOT devices are pretty low bandwidth, so I doubt they'll be taking up much cpu/ram to handle them.
For smarthome, I would recommend Zigbee devices. That way, you limit your attack surface to just your Zigbee gateway, rather than every single light bulb in your house, with the added benefit that those don't clog up your Wi-Fi.
We have the Philips Hue gateway at home (which has limited support for other brands, but IKEA Trådfri bulbs work), but you can also get a Zigbee USB stick/Raspberry Pi HAT, install Home Assistant or deCONZ, and go wild without being tied to any vendor.
Why would you want to cram 50 so called "smart" devices is the real question. Is your quality of life improved by having your lightbulbs and switch connected to the internet. Why do you need sensors at all?
My home is completely analog, like I even have to operate my windows blinds manually. I have lived in a totally connected and electrified house and I didn't view any improvement in my quality of life. Only downsides when the power grid had an issue.
Well, if you want an example, I have about about a dozen PM and CO₂ sensors spread around the apartment, and some outside of it. I live in an extremely polluted area and it allows me to make decisions on when it's (relatively) safe to open windows (or even inside doors if it's really bad outside).
PM 2.5 may be in the range of a couple micrograms/m³ in one room (with air purification) and 100× that in the other adjacent room, so it makes sense to have sensors everywhere.
You don't need to have it internet connected to have your thermostat on a timer. My home has responded to heat or cool the house based on when I wake up, when I leave, when I come home, and when I go to bed for well over a decade all without needing an internet connection to do so. My thermostat doesn't go dumb just because the internet went down or because it became unsupported and got bricked.
The only thing I wish it would do would have better multi-zone temperature and humidity sensing to know to turn on the circulation fan when the edges of the house get too hot/cold compared to where the thermostat is. Even then that doesn't require the internet, it could be done with cheap 433MHz temp/humidity probes running on button cell batteries for years.
I tell my thermostat my schedule once and how I want my house to be, and it makes sure to hit those temperatures when I want it to. I shouldn't have to "tell it" I'm coming home, it should just do it.
Respond to the weather? Its a thermostat. Even a decent bi-metallic strip thermostat will "respond to the weather". Its not like the thermostat needs to do anything different if its an especially cold day outside, it will keep the indoor environment as you programmed it. How do you think thermostats worked before the internet?
The only "respond to the weather" idea I'd like would be to account for especially humid days as sometimes the temperature is fine but its really humid in the house. But once again it doesn't need to reach out to an API to figure out the humidity outside at some airport 20mi away, it just needs a local humidity sensor.