Learn French: Toi, tu es un frère pour moi. - You, you are a brother for me.

In French, you can double up pronouns for emphasis. Toi is a stressed pronoun used to highlight who you are talking about. Using Toi, tu is like saying 'As for you, you...' or simply putting strong emotional emphasis on the word 'You' in English.

Why is it pour moi at the end instead of pour me or pour je?

Whenever a pronoun comes right after a preposition like pour (for), avec (with), or de (of/from), you must use a stressed pronoun. The stressed pronoun for 'me' or 'I' is moi.

Is it mandatory to include Toi at the beginning, or could I just say Tu es un frère pour moi?

It is completely optional. Tu es un frère pour moi is grammatically perfect. Adding Toi at the start just makes the statement more expressive, which fits the warm and affectionate feeling of the sentence.

Could I use vous instead of toi and tu for this sentence?

You could grammatically say Vous, vous êtes un frère pour moi, but it would sound a bit strange. Vous is for formal relationships or multiple people, while calling someone a brother implies a very close, informal bond, making toi and tu the natural choice.