"How are you doing, Marcus?"
Translation:Quomodo te habes, Marce?
Is the "te" necessary? I thought pronouns can be dropped if the verb makes it clear.
It is necessary here. Without 'te', the sentence would mean "How do you have, Marcus?"
So instead it is something like, "How do you have yourself, Marcus?" Sorry, just trying to get it.
I thought word order didn't matter as long as everything was in its proper case? Why does it have to be "...te habes..." and can't be "... habes te..." ? Just curious.
Word order does matter in the sense that there are common expectations for how classical Latin is written. It is most common for objects to precede subjects, for instance, thus "te habes." Authors can play around with this to some extent, but to say that Latin word order doesn't matter is a misrepresentation of how it was actually used in written prose.