More extreme weather

For rain to be useful it needs to be consistent and predictable.

If it only rains on 1 day a year, and on that day you receive 1 years worth of rain, it just washes all the soil away.

From what I've read on this, hot-dry places will get hotter and drier, with intense desertification. Places that are typically wetter will have more frequent bouts of flooding and unusual rainfall patterns, like places that traditionally had "balmy' weather might experience sudden 40day+ continuous heavy rainfall.

Also, even though on a whole the world average temperature will increase, cold weather will also tend towards the extremes with longer, colder periods.

Yes and no, sometimes one after the other. Climate change is more about the climate destabilizing and becoming more erratic as opposed to moving in any particular direction.

Here you can see the effect of increasing global temperature on precipitation:

https://interactive-atlas.ipcc.ch/