Also how to prune and when is it safe to? And how do I make sure I don't cut too much off?

In what part of Oz land do you live? Can you put your Meyer in the ground? They are much easier to deal with when planted in the ground. Pictures would help, of course. If it is in a pot now; and you are going to plant it in the ground, you only have to dig a hole a little bigger than the pot; carefully take the tree out of the pot (for me I always choose to destroy the pot to preserve the rootball) and put it in the hole. Back fill with the dirt from the hole , water it in well and wait. When it begins to make new growth you can begin a regular fertilizer regime; but not before; the absence of nutrients encourages the roots to grow seeking food and water; and with citrus, first the roots grow and then leaves and branches.