For instance, as your building track some distance away from any city (or town?) can a player put down a piece of complex track like this and not connect to the other section of track?
No. Each piece of track you put down is owned by you (at least for the time being), and must be traceable back to a city following your own track. You cannot lay down 'orphan' track. So, in order to lay down 'complex non-town tile' you must be in a situation to still satisfy these requirements.