It's really easier to do using modern programs like photoshop or gimp(though probably not faster than pixel art by a pro).
First, I quickly, sketchily try to get the concept in, rescaling if necessary to adjust with the other characters. Then, I put black around, because it's easier to see the color brightness on black. I apply a soft gray shade to remove most pure white areas because they generally don't react well to color modification layers such as curves or overlays. Then I apply a generic color base that I use for all characters, to unify them somewhat, before applying a first color overlay using picks from the concept. Then it's just a rendering process, adding detail and balancing the character. I might change some minor things in the posture but I usually try to avoid that, because it can lead to mistakes that will eat up your time away.
I try to work on a lot of things at the same time, bringing everything forward at a pace, like a printer, to avoid slaving like crazy on a single character then finding out I have to do the rest. Also, I often discover new techniques along the way, that I can apply to the older work since it's not necessarily to far gone ahead.
The golem was a bit harder than it seemed at first, because there was an added challenge in getting a dry clay look, and making him seem as detailed as the others meant small cracks, things like that.
Once I have the first frame of the idle though, I use it as a reference for the other frames of the set. Here I use it as the first frame of the walk cycle to help in looping.
Copy pasting the various parts, I set up a first cleanup draft. It will make it easier to polish the rest, though I want to have proper rotating arms and legs, and not the cutout look such a technique would bring if left at this stage. You can compare with the final walk set...once it is done
One last tip. When I am doing crazy detail in repetition, my mind starts to wander , but I want to keep it doing, well drone work. I use half of my screen to watch bad horror movies(or whatever works for you, anything that does'nt require heavy brainwork or attention), so it occupies the part of me which want to play and entertain itself. It shocked a few people when they saw me doing this on my day job, but they can't argue with the results at the end of the day, so they leave it alone.