Should I just create a completely new post when updating my questions?

If the "update" is significantly different from your original question, then yes, it might be a good idea to start a whole new thread. If it's just a minor clarification, a reply will usually work. Either way, it's considered bad form to change a post without (1) leaving the original intact (though sometimes <strike> is used to indicate retracted parts), and (2) clearly indicating an update has occurred. See 'How do I change/delete my post?' for more explanation.