For your first Sculpt, it's looking really good.
My suggestion is to get as many screencaps of Count Dooku, and use them as reference, also if you may try Ebay you may find a lifecast of Christopher Lee and use that as reference, there's no better reference than a real lifecast.
It may also help to work on one area at a time since you are starting out (instead of trying to do everything all at once), start with make the ears more realistic, then the nose, mouth, eyes, etc...after you have matched everything to your reference pics then you will be on your way to having a very realistic likeness.
I personally use one light source to make sure that each angle of the face matches the ones in the photos, trying to match the lighting (on your sculpture) to the photos will also help you match your sculpt to the real face.
The Oil-Based Clay is fine to use, just make sure if you mold it in a Silicone that it's NOT a Tin-Based Silicone because Tin-Based doesn't like the Sulphur in Oil-Clay and will not set up and remain gooey.
PS:
I forgot to mention that for the eyes it is easier to use spheres as the eyes to sculpt the eyelids on, that way you don't have to repeatedly try to sculpt the eye shapes from scratch.