I don't see "Ou vas tu?". Is that considered very informal or wrong?

Bonjour Steve !

Not at all : "Où vas-tu ?" is the inverted question form, which is actually considered more elegant and formal than its equivalents:
"Où est-ce que tu vas ?"
"Où tu vas ?"
"Tu vas où ?"

See the related lessons:
https://kwiziq.learnfrenchwithalexa.com/revision/grammar/forming-questions-by-inverting-in-the-present-tense-except-il-elle-on-forms
https://kwiziq.learnfrenchwithalexa.com/revision/grammar/how-to-ask-questions-with-qui-que-quoi-quand-ou-comment-pourquoi-and-combien

I hope that's helpful!
À bientôt !