0°C is absolutely super practical and is imperative to have as a landmark. 100°C boiling water... it isn't really that practical in day to day use in my opinion (when was the last time you saw 100°C written on a device?). In the high temperatures the ones I care about in a practical sense are on the oven for cooking and on my soldering station, both much higher than 100°C anyway. The only time I care about boiling water temperature is when I am boiling water in which case I don't need a thermometer.
So I think 100°F is more interesting as a landmark than 100°C for intuiting temperatures. You can think of it as the percentage of how hot it is. But 0°C is more interesting than 0°F.
It doesn't even matter much for meters and kilometers, since I very rarely need to talk about things that are kilometers away and meters away in the same context. It's handy to have sane units for those, though, since there you can multiply and divide in your calculations.
Temperature arguments never seemed particularly compelling to me. They assume 100 is more convenient, which I find wrong, since you're usually talking about 102, 86, 95, etc anyway.
We use 0.1°C for even better granularity. E.g. weather sites, all my digital thermometers, etc.
Daily. Ovens in Europe typically will have a temperature range that's something like 50-400 C. I've never seen oven without a 100 C setting. Sauna thermometers will typically go from ~20 degrees to either 120 or 140 Celsius.
One decimal place is commonly used.
Which exactly? Walter melting at 0°C and boiling at 100°C seems the most practical.