i went extra with my answer and i have 4 joshua fics that i've read recently and really love, all are joshua ships; some are joshua pov some are not. because i think is a rlly interesting character to write both from his pov and to write him from someone else's pov.

uncommon language by dykyeom (javasleuth)
https://archiveofourown.org/works/82601086
haoshua - xmh pov
insanely brilliant characterization of everyone but especially junhao's dynamic and this is such a Joshua. so many lines had me reeling and pondering. i think the juxtaposition of how similar yet different haoshua are lends itself rlly nicely for any sort of character study and this is such a perfect execution of that.

fire breathing factory by pinkish
https://archiveofourown.org/works/87065411
another haoshua !! hjs pov
i read this recently and i keep meaning to try and leave a comment but i still havent found the words to describe how it made me feel, even still. the booshua dynamic is such a lovely one, so is ofc the haoshua - i think pinkish writes one of my favorite iterations of haoshua - but also the subject at hand and how its explored and the character progression of jisoo and her own relationship to gender and queerness. i think joshua is a really fascinating character to explore these themes with and this is such a beautiful and hard-hitting portrayal of that

but i do, i finally do by infrequency
https://archiveofourown.org/works/59175373
gyushua - past vershua - hjs pov
this fic is like made in a lab to awaken the evil demons in my brain (joshua ult who has past lives in letterboxd top 4). its so achingly tender and a lovely exploration of being a second gen immigrant and the dynamics of the relationships this joshua has with the people he has in his life and what these relationship represent (with hansol with mingyu with his mom to korea to california with korean as a language)(the many shades of who joshua is). just so so lovely.

triangles by miuyi (rainiest)
https://archiveofourown.org/works/59706151
shuahan - yjh pov
i brough it up in the beginning but i really do love reading joshua as the love interest (and not just bc i like reading descriptions of him) but i think it's nice to see him from an outsider pov. he's a nurturer, someone who's steady, he bleads care and is so delicately sincere. i think especially in the context of jihan it works exceptionally well bc of how their relationship is. i hold this fic very near and dear to me.

i love aus but my preference with writing will always be canon comp.
this is just my own opinion, but i write svt fics because im so intrigued by the dynamic they have with each other and who they are as people and i love to explore. and as much as i do love an au (my first two fics are aus) there's something about canonverse that i think hits different; these dynamics are at their most potent. i also think there's more potential for character study type of fics in canon comp fics which is something i love writing. there's also the more behind the scenes fics where you can build off a moment that happened and satisfy that lil fushoji parasite (one of my favorite canon fics builds off the haoshua kiss in a live) or explore what a relationship progression can look like with someone who is your coworker and friend where there's so much responsibility on the line and the naunces of that (there's a brilliant soonhao fic that explores that) or even piece together canon moments together which i got to do with beta cancri. it's also really infromed by how i watch svt content? like so much of my fic ideas happen when im watching gose or in the soop and i get inspired! also the worldbuilding element, i really love being able to reference certain moments and details much more than building an entire fictional world in an au. moreover i enjoy doing ensemble scenes and i think the (platonic or even more) dynamic of ot13 is near impossible to replicate in the same capacity in a noncanon setting.

im of the opinion that a slow burn is less of a specific word count thing and more of a percentage. like a slow burn's resolution, in my opinion, is ideally after the 80%-ish mark so if its like 15k words it would be like 13k if it was like a 80k fic it would be at 50k-70k ish. that being said i do think the optimal word count is such a hard concept to quantify because like each person has their own preference for their preferred length to read. like i think for me the sweet spot is around 10k-40k, but also ive loved 300k fics that were slow born and ive loved 1k fics. all that aside i think as writers we place too much weight on word count in a way most readers dont? like i rarely actively find myself checking the word count for fics when im reading as much like tags yk?
also another factor is like how verbose vs concise someone's writing style is. i think two people can both write a great slow burn and one would be 90k and the other is like 30k.
the hallmark of a successful slowburn is like creating prolonged and intense buildup and tension and pining to the point where you or the reader has to be like omg kiss already. because slow burns are about delayed gratification and the anticipatory factory.
i hope this helps ! i also think having someone else beta read and offer their own perspective is also really helpful in gauging if it feels satisfactory.