yes, because a sith lord is a higher rank than standard sith i believe. If you wanted a military rank i'd put that in the sith OOC board to see what other sith think of it. I would think 'marauder' is the title itself.
Depends, I can see an imperial of lower equaliant rank referring to them as Lord, but unless they are in fact a sith lord I doubt another sith would call them by that title.
In this situation it is a commander. Also, somewhat off topic but I figure I may as well as now, do I need permission from the FL to give my Sith a corvette? The rules aren't clear in this matter. He is an old sith so I am unsure.