A marquis is similar to a count (basically, you rule a piece of land and you have subjects of your own) however the difference is that I believe a marquis was ruler of a march, a border-territory that was intended as more of a castle where men could be stationed in case of war. If you want to be a very minor noble then you'd be a courtier (someone that roams the court of a noble) from a noblemans family.

And yes that's kinda what I was going for, just using them as a basis for appearance and then letting everyone just come up with their own version more or less. :P