So I was asking for some advice and I got this:
retopo this immediately, its abysmal. Use low poly to drive a subdiv or multires, and add geometry as needed. It's literally unworkable at this stage.
Of course I now know that I shouldn't have started with a UV sphere but it was kinda too late and only really cause some (invisible) problem on the top.
It's my first model of this kind, I only have 216h of blender (thx steam for the counter). The vertex painting is of course horrible and it's just a visual guide and will be deleted ASAP.
What my friendly reviewer didn't tell me is "why?" and, if I "retopo" the model (I won't, I'll restart from scratch), what must be done in order to not be a disaster. I tried hard and spend many hours trying to keep the quads "clean" instead of hacking my way with the sculpt tool and dynatopo. If I just wanted to sculpt I would have used oculus medium, but I want to learn blender too.
I wasn't quite ready for such a hard comment but I got over it (it was yesterday). My problem is, if I had to do it again, I would do it the same way (I would start with a quad sphere instead of a UV sphere but that's all) and it's apparently the wrong way. And I can't imagine any other way to do it.
I understand also it has too many polygons. I started with a lower resolution but once the general shape was complete I applied the subsurface modifier and started refining the model and this is what's shown in the picture. I shouldn't have applied the subsurface but I'm not sure it's what makes it "abysmally bad". Therefore, what's wrong with the topology and how to not repeat the same mistakes, whatever they are ?
EDIT : I'm asking this because I'm stuck in my process now. Because I know I'm doing something incorrectly but I don't know why it's incorrect.