Thanks to both of you. Since this is a new technique to me (along with portraits in general!), I know there's lots of room for improvement so I thank you for your encouragement.
Faisal, you can do the same with oil paints but the decision to blend or not has to be made sooner than with gouache. The real perk with gouache is that they dry like acrylics but can be moistened and changed or even removed in some cases even after they've dried. That gives you the ability to work out what you want in your oil painting before you paint.
If you do go with gouache, it's way cheaper to go with a limited palette and I recommend either Schminke Horadam or M. Graham gouache as the others either re-wet too readily making it harder to blend or just aren't as pigment-rich as those two. Both are pretty expensive for such small tubes but I think more economical in the long run. Cheap synthetic brushes work best as the gouache destroys them fairly quickly.