It's a bit hard to work toward likeness (if the goal is a very realistic portrait of a well known person) because of the significant changes in all the proportions between orthographic projection and perspective views. You align everything in orthographic front/side view, but once you start looking from other angles the view switches to perspective and everything becomes super distorted compared to orthographic. And it makes it a bit hard to check it with references that all facial features are correct. Any tips for that?
Well I've heard Kent said multiple times to try and not sculpt in orthographic view, because of the lack of perspective and things getting squashed, and that even though it's uncomfortable to sculpt in perspective, that that's where you need to put the effort in. That it's not about making a copy as if your doing a CAD blueprint of a building, it's more about letting your wrist loose. In time you'll start to get your eye to match what your seeing with what you're sculpting, it just takes practice. I guess it always helps to have the reference visible and take breaks, because you get so used to what you are seeing that you loose your frame of reference. If you take a break, when you come back you can see the errors more clearly.