That looks great! One of your advantages is that you can easily try out different ideas since you are using digital art. You should make some thumbnail sketches, and use some ideas from other portraits. Try out a lot of different things, because your first one isn't always the best. You can create a new layer(or duplicate the layer as a backup), and paint the one that looks the best. If you don't like it, you can do it again. Looking at some reference can also help if you don't know anatomy very well. I hope that this helped :)

I also am doing blender, and I agree that it is an amazing software. These are two tutorial series that helped me a lot: https://www.youtube.com/watch?v=bpvh-9H8S1g&t=5s In this one, they teach you a lot, and in the process, you make a cool sword scene. https://www.youtube.com/watch?v=TPrnSACiTJ4&t=749s&ab_channel=BlenderGuruBlenderGuru This one is also a really good one. In it, you make a donut scene. This channel makes a lot of good videos on using substance painter and blender together: https://www.youtube.com/c/StylizedStation/videos But, I would suggest doing the other ones first to get a better understanding of blender before moving on to this. This is a good tutorial from them: https://www.youtube.com/watch?v=d7XJjftEaK8&ab_channel=StylizedStationStylizedStation getting a good understanding of nodes for materials can help a lot, but might not be very important if you are just using it for concepting. I can't suggest a whole course for it, because I picked it up as I was learning.