I would separate about two hundred of them from the rest, separate that group in half, and tell one side to go out and research immortality in a scientific way. And the other half to research immortality in a mysticism way. If nothing can be done, I have them pool their efforts into one big project that combines science and magic, for the single goal of getting me, and my trusted lieutenants, immortality. (Though I may give my lieutenants a weaker version, where while they won't age, if they are killed physically, they can still die. I may consider giving them better resistance to damage than is humanly possible though. And I may allow my normal servants to live up to half a millennium. Only if they prove hard working. If only because it is such a chore to find good help.)
I would have one hundred of the three hundred that are left as my personal servants. For now, and I would send the other two hundred out converting others to my cause. If I gain immortality, and the process of conversion is slow, I shall demonstrate it. It can only help.
I would then go to TVTropes, copy and paste every page having to do with the "Evil Overlord List," have it set up in an easy to follow guideline, and make as much use of it as possible. As I would totally be an evil overlord. Hopefully with immortality. (Parts about harems and such may be ignored, if I so still wish, once all that power and evil laughing have gone to my head.)
Edit: I would have NO CHILDREN. If I must get rid of desires the old natural way, I shall make absolutely sure nothing can come from it. I don't want my followers defecting to my child, or them trying to overthrow their old man one day. I want to have my immortality and power as long as possible. Forever if I can.