You need to understand, that when you tell me to add an HDRI, I will first google how to add an HDRI.
The most I have done is played around with different kinds of light objects that are available in the menus.
The moon part is easy. I have made similar stuff. I'd say 15-20 minutes for that. (Yeah, I don't remember any of the shortcut keys)
For the body, I see that I'd just need to make some pipes and rings and that box on the front and the backpack, easy peasy. 7 hours.
I would have done that part faster in AutoCAD.
The face?
I can't even draw faces.
Give me 2 days to try ~150 iterations to get something satisfactory.