What are the four elements need to be balanced?

Answer 1

You're referring to the Galen "elements" of Fire, Air, Water and Earth? They have respective characteristics of hot-dry, cold-dry, cold-moist and hot-moist; it's these that theoretically need to be balanced.

Incidentally, a very similar structure in the Far East employs five elements: Earth, Metal, Water, Wood and Fire. Metal was originally Air, and Wood is the only living member of the combinaton. In the Asian system, ech Element "generates" another and "consumes" another. One can play a sort of expanded version of Rock, Paper, Scissors with them:

Water overcomes Fire, obviously

Earth overcomes Water (by absorbing it)

Fire overcomes Metal (by melting it)

Wood overcomes Earth (growing out of it)

Metal overcomes Wood (chopping)