As for the belt ... It's something that is left over from MoP, when i first made this set. I kept it because it does a good job in breaking up the blue from the lower parts of the robe. The Primal Mooncloth Belt looks good with it but i'm not a fan of the 2D stuff and it leaves a lot of blue on the robe exposed which i don't like. The Fearless Gladiator's Silk Cord is also a cool replacement, but i don't like the placement of the belt and how it exposes where the tabard is cut off. The 7th Legion stuff also looks decent, but they are very high resolution compared to the rest of the set, and it leaves far too much blue exposed.
I find that the cape compliments the shoulders extremely well, with the golden/yellowy parts seemingly flowing out of it on the sides. It is a tiny bit off color and has a more metalic(?) shine to it, but i find it a much better option than any of the other blue capes. They are stronger blue color, but don't play off well with my other pieces at all. Not having a cape is not an option for me. The movement feels very odd without one as a gnome. It feels much heavier as there is more focus on the hips, rather than a cloak floating about. :) It might suit taller races more.