I don't know if "bo" is used in colloquial, everyday speech.
yes it is, very much so. A stiff and unnatural equivalent would be "ponieważ".
A: Przepraszam. Czy pan tu mieszka? B: Nie. Dlaczego pan pyta?A. Pytam, bo szukam ulicy Ogrodowej.
It sounds all right. In order to make it more colloquial I'd just cross out
pytam in the last sentence - just:
Bo szukam ulicy Ogrodowej.The second dialogue is fine too. Two things that sound slightly off are:
Janek: Czy masz trochę czasu?
Czy is rarely used in everyday speech as the beginning of a question, it's usually omitted.
Masz trochę czasu? is more natural.
co słychać u ciebie.
co u ciebie słychać - it's better in that order, but anyway it's fine and no more stiff than
co słychać.