tu is used in the south of Brazil. which is a minority of Brazilian Portuguese speakers. You can get by without ever using tu. also indo is used for you will be physically going somewhere. there a slang phrase that means im going or my leaving. tô indo

You can find the standard which is applied in any Portuguese speaking country here: https://www.infopedia.pt/dicionarios/verbos-portugueses/ir https://www.conjugacao.com.br/verbo-ir/ However, in some regions, in oral language, some Brazilians say "tu vai" instead of "você vai" but it is not considered standard.

The second one is right, tu vais. However, if you use 'você' you should say 'vai, without 's''.

quem gostaria de ir pra praia?

The conjugation of the verb to Go in present in portugues is eu vou tu vais ele/ela vai nós vamos vós ides eles vão