In percentage that means how much? I mean m so far you did some good job. So if you can sort this out and you actually get them into the game. You will be a well renowed writer. Thats for sure.
Im not saying all is perfect. Atleast in my taste the horse one is weird. But the rest of it is quite good. Specially the frost pup.
So my general process is this:
1. Character with either low scene count or incomplete option for top/bottom, masculine/feminine. I wanted to start off small/underused. I looked through the wiki, zoomed through the sex options for the characters that I thought needed content, and went from there. I then try to match the writer's tone, or spirit at least prose wise.
2. What is missing/players have asked/want? For the horse, I'm assuming the shaman, there's an anal scene where you get cucked? I guess, but there's nothing for the player character getting dommed by the she-stud variant. Thus, I chose to do that because I know there are players who like that sort content of sub/bottom content. It might not be your cup of tea, but it's a scene designed to appeal to those who like that sort of content.
3. Redundancy: I'm not a fan of doing x variant for characters. If there's already an identical scene, that I won't bother since it's a waste of time. There's little point in having two doggystyle scenes for a character unless the feel/vibe is completely different. I'd probably do another position/some act in line with the character's persona/prior kinks.
4. I don't have a dog in the fight. I'll write hetero, yuri, gay, so long as I feel I can do it. So for me it's not about who, but rather what needs doing. As for percentage, I have no idea. My goal is honestly to write between 15-30 scenes the next 2-4 months for any underused characters since I do this as a side hobby to my main business/other works. On a good week, I can do 3-5 scenes rough, polished, and submitted on 1-2 week time table. Keep in mind I have written an event or two, some long-term pipe projects (which likely won't be approved/considered so I'm only outlining/pipelining) but haven't posted them yet.
5. I have 9 scenes submitted at the moment. Keep in mind they likely won't be reviewed for months potentially. And in the off chance they all do get approved/coded, if I was implementing them, it'd be dripped with each update so it's truncated.
As for characters, it's about priority accordingly:
1. Companions/Main NPCs: Most of the core companions already at barely halfway through the game have a plethora of scenes. I've no real interest in adding/writing for them at moment. Not because I wouldn't write for them, but because their writers have content pipelined for them already for the next 6 months to a year. Again, it's a waste of resources/time. I'd be better off allocating my time to what I am targeting.
2. Regional Waifus/Side Characters: Your Atanis, Amaris, Hrethas, etc. My bread and butter are the regional love interests/semi-committed lovers who don't have as many scenes. Again, my issue is that these characters are already content heavy or in some cases content complete. I know some players would love to have say 10-15 scenes for every NPC/side character in the game, but that's a lot of work/not realistic. I'd say any side character in a main area -- the War Camp, Khor'Minos, Hawkenthorne, Kitsune Den -- really doesn't need more than 5-8 scenes.
3. Enemies: I like enemies but again some of them are content complete. And some like the Earth Elemental are just random encounter fodder.
As for me, I personally, if given the chance, would like to write tainted/corrupted options. But for me, I'd like the corrupted/tainted/dark knight persona to be less hedonistic fuck machine or insatiable pit of lust, and more cold-blooded/ruthless rival or the very least in control. Corruption to me works better when it's the control of a top or the control of a power bottom, which is why some of my scenes have a dominant/dominatrix with slight sadism or the very least teasing/taunting nature. I'm more lawful evil/neutral evil than hedonistic Lethicite producer.