Hi and welcome!
I think there are a few things I would like to comment on that may make it easier for you to manage all that information and get a satisfying image:
1) Painting against white is lethal unless you are doing something with a lot of contrast -- strong lighting. So paint on top of a tone if not try blocking in some shapes to accompany your drawing.
2) As to the pose, if you are interested in capturing a character, body language says a lot. And this is very exposed and dominant -- like something I would expect to see Spiderman or someone highly physical do. Gollum seems like a cowering creepy slinking distorted character, rather than someone with this obvious comfort with his body. So I might consider using his pose as a way to show character, especially in one single shot of him.
3) I would perhaps consider using your light and shadow to exaggerate this schizophrenic split personality -- so since you are into comic books, I figure you are acquainted with some of the darker subjects. Bernie Wrightson is a very good example. Frazetta too for showing shadowy villains. Often times they will have almost the entire face in deep shadow in order that they can do glowing, predatory, leering eyes. It's definitely a cheat, but it works.
So I would recommend that you cut loose and let your imagination run wild and use all the graphic tricks at your disposal.
I think the portrait of Gollem that you did is great as a reflection of the character in the LOTR movies. It resembles him. But the film makers have the benefit of time and action and story, whereas you are telling all that in one picture.
I can see you have skills from the good line drawing you show here, and you certainly have a huge visual catalog of past comic work in your head to draw from. And I think you can really take your work straight to the top once you get past the getting your feet wet with the software phase.
"Not a bit is wasted and the best is yet to come. . ." -- remembered from a dream