@haith92 As far as proportions in characters go, just steal it from other artist lol. Steal in a good way. For example, if you want to make a fat pig character like roadhog from overwatch, then take roadhogs proportions and modify them. This is what I did for a design I'm cooking up.
I wanted to make a stylized male character with a big frame so I looked at the marine characters from SC2. This is something I've never really done so I wasn't sure how to do it.
Side note: I also turned the silhouette into a brush to make it easier for future cases if I wanted to make more characters with similar proportions.
You can take it and use it if you want.
Now I modified my silhouette to fit my taste better.
As for armor designs, once you understand the basics of real armor designs, it comes down to the silhouette, When you make the silhouette, reference animals, bugs, or other shapes you find in nature.
Here's a quick female silhouette along with some quick designs based off the different bugs on the left
From there I make the silhouette of the armor using some bugs as a base. I mix 2 or more to come up with different results. You can turn the bugs all black and lay them on top of the base body and modify as you go.
The details can come later as well as making it more armor like using reference.
As far as not getting the curvy girl look, try using more hard planar shapes. You can use things like a triangle or cube like shapes more as your shape language, Or try to use shapes that hid the curves of the female body. Or you can make her a body builder type like zarya from overwatch. The shape of the base body effects the design over top so start there. Just use some reference to get a different look.
Hope that helps.
Because of this I actually like the 2nd armor design I did so I'll push that one in the coming future.
I hope this wasn't too long of a read.