When I get refs, I usually like to get front view, back view, colors and a little bit of text letting people know the character's name, species and anything else that might be important.

However, I wanna say that if you don't enjoy doing refs or customs very much, you shouldn't do them, regardless of how many people are interested. It's important to make sure you enjoy what you're being asked to do. That's just personal opinion though.

I like having a front and back nude ref and an alternate version with the character clothed that I can use as a sfw ref. After a swatch of the characters colors and then a bit of text with the character name, species, and other relevant info. Anything beyond that like detail closeups or headshots of various expressions I can take it or leave it.

Front and back view at the least, I have seen other artists starting to offer options to them, like in addition to the front and back view, the customer can choose to add on things like a close up mouth shot, close up of hands/feet or of special markings/tattoos/piercings, or close up genital views. Those are some of the more common, but also accessory views and clothed/nude versions.

But if you don't enjoy making them then you probably shouldn't consider it, you might end up making yourself unhappy and that would suck.

No shading. This is a ref sheet, not a artwork. The colors should be clear, special body markings highlighted if possible.

As nice as that would be, your time would be better spent doing other things. Reference sheets are better done simpler, whereas you have such talent for dynamic posing and shading.

At the end of the day it depends on the characters design but a ref sheet only feels complete when it contains four things:
A flat colour front fullbody;
a flat colour rear fullbody or half-body (depending on the symmetry of the character's design;
a flat colour headshot showing the eyes, teeth and tongue;
colour palette(s).
All other details are non-essential bonus.

Essentials are front and back, and any markings that warrant special attention like tattoos or body marks~
non-essentials/paid bonuses that I love to see are little chibis on the side to showcase outfits, close ups/headshots, and doodled likes/dislikes~
and personally they always get kudos when they do dynamic or personalized poses for them to really show off the characters personality, but I know that isn't always the easiest to do with refs

that SAID, if you genuinely don't like to do them it'd feel weird to order one from you just because then I'd feel like I'm contributing to your art/personal stress. You don't have to do anything you don't like to do just cause the masses want it, it al depends on yourself and what you want or think you you can handle at a time. Customs can be just as rewarding and fun to do as they can be frustrating and annoying and it entirely depends on the person or character they have in mind. Just do what you feel comfortable doing~

I mostly just look for front, back and side views, and various facial expressions. It doesn't need shading or even coloring.

Front and back full body, flat colored with a section dedicated to the character's colors. Don't need much more, but if an artist provides more, I don't mind picking them.
A SFW and NSFW version is nice too, a bitless and bit version (nips and genitals.)
The expression on the full body can show off the teeth and tongue if they're different from the normal.
Text putting the character's name and whatever else they want.