suchtie

Well you can, for example, ask how many pencils would fit in a bathtub. And how many goats you would need to have the weight of these pencils.

Warm water cools down even faster than cold water due to evaporative heat loss. As long as it's not -40 °C or colder then water at 1-4°C works alright. 30 °C water would freeze before it touched the ground.

Exactly.

Potatoes are vegetables. They are roots, just like carrots or asparagus, which are also vegetables.

Mushrooms of course are neither plant nor animal, they're their own thing. Actually they are more closely related to animals than plants.