>>23451748
I've sculpted something for almost every groupbuild entry I've done. I find it rewarding, but the right material that suits the artist is very important. Many swear by Kneadatite (Green Stuff) as a sculpting medium, but I find like it working with old chewing gum. It's rubber-ness is a reason miniature sculpters use it, as certain techniques require it's "flex". Myself, i always use Apoxy Sculpt, as it dries rock solid and I can sand away any mistakes after it cures.
If you need sharp edges, use styrene sheet (plasticard) and smooth/sand the putty right to it.
As for symmetry, the Grimzock here is terribly asymmetric, but I was able to smooth it by spray painting it an even colour then sanding away the paint. Every peak gets sanded away first, and any valley can be filled if necessary.