If you plan to use this to make a human model, not just a dummy, I would not take this approach to modelling it. Your image can work okay as a reference for the overall shape of the body and the proportion for the had, but for an actual human face you’ll have an easier time with a proper face reference and even if you don’t plan to animate it, the model will be easier to work with if the topology follows the face.
For your first character, I recommend following along with a human modeling tutorial. It’ll make it easier to get the topology right, and make it easier to do your own thing for future projects. Recommendations:
All of these are female characters, males can be similar topology-wise, just follow male ref material. If you just want a basic face topology guideline instead of a tutorial series that’ll take weeks to follow, this image could be useful:
You can find lots of reference if you search for “face topology” “character topology” “body topology” etc.
I feel I should also warn you the arms’ A-pose is a bit extreme as well, so if you model them with that low of an A, you may have difficulties when you rig it if you want the character to raise their arms. A pose will make it easier to get natural looking shoulders with the arms down than T-pose, but this might be too sharp of an A.
It’s generally more professional to sculpt then retopologize, but I think polymodeling is a lot easier for beginners just getting started with character modeling, and a hybrid approach (where you polymodel the basic shape then sculpt) is easier than starting from a sphere even with experience. Whether the hybrid approach requires retopology or not will depend how careful you were with the topology for the base. Starting from a sphere is pretty brutal, in my opinion.