Would you add me on facebook > Voce me adicionaria no FB no?
Would it be more natural to use the present simple here me adiciona instead of the condicional or vai or future in spoken portuguese?
You are right. The correct translation would be "Você me adicionaria no FB?". On the other hand, it sounds less formal if you use present simple. If you want to be polite, you have to use the conditional.
I would LOL if she pronounced Facebook like it's done in Brazil. "Fayceebuk" or just "Faycee" :)