how many cases can be present in one sentence?
In one sentence can there be nominative, accusative and dative in the same sentence? Is that usually how it is? I don't know if this makes any sense but thank you :P
You can have ALL cases in one sentence :)
Wegen des schlechten Wetters (genitive) gibt der Mann (nominative) dem Jungen (dative) einen Regenschirm (accusative) - Because of the bad weather, the man gives the boy an umbrella.
A complete sentence must at least have a subject in the nominative case and a predicate. That's the minimum, e.g. Der Mann (nominative) liest.- The man reads. In very colloquial speech, the subject can sometimes be left out, but that's not standard German.
Then you can add a direct object, usually in the accusative case, e.g. Der Mann (nominative) liest ein Buch (accusative) - The man reads a book.
With some verbs, you can add an indirect object in the dative case: Der Mann (nominative) gibt dem Jungen (dative) ein Buch (accusative) . - The man gives the boy a book/The man gives a book to the boy. When you have two objects, the direct (accusative) object is normally a thing (here: a book) and the indirect (dative) object is normally a person (here: to the boy).
Also, you can add any number of adverbials whose case depends on the preposition used in them: im Haus (dative: in the house), trotz des Regens (genitive: despite the rain), ohne den Regenschirm (accusative: without the umbrella).
Or you can add a genitive by talking about possessions: Sarahs (genitive) Buch; das Buch des Vaters (genitive) - Sarah's book, the father's book.