I try to keep the lore pretty accurate to the original Youkai. Of course, I take a few liberties to account for Touhouisms. The Mikari Baba for instance is canonically a hideous old crone, with one eye and carrying a burning rope in their mouth, wearing straw rain coats. This on the other hand, is the image that inspired Agappa-Chan. She was made younger and given a yellow raincoat to make her more cute. But I try to make any original Youkai true to the spirit of Touhou, and its Animification Beam. Some choices I make are more for fun, but are rooted in Youkai lore. Its a fun way to characterize, and humanize them in a similar way to Kogasa's humanoid form. Their personalities on the other hand are fairly rooted in the original lore. Even if the Hitotsume Kozo are themed for the Three Stooges.
I've a long interest in folklore, whether American, European or Asian. Youkai were an interest, even if older books tend to only have really famous youkai. Wikipedia is an option, if you skip the article and go to the citations. But yokai.com is the best resource I ever found. (Side note, Touhou resources tend to use 'Youkai', though the more accepted Western transcription is 'Yokai'). As for my knowledge of the series, I'm definitely a casual fan as far as the games go. Gri would kick my ass any day of the week. My introduction to the series was actually through fan games, even if I had distant contact with the series since the 2000s. I found a Touhou mod for Mount and Blade, and that led me to the Wiki. I talk about the lore with people from the site and read/watch lore info dumps. My goal is to show a scene to a diehard fan and have them nod and go 'Yeah, my favorite part of Touhou's just like that'.
I'm not sure OoCs would be welcome in fan works, and I think Misty Lake is a better place for my rambling replies. But I can tag you if it helps @kymoh.
I was hoping to surprise you guys with a reply already. But tomorrow I'll be a busy man. Hoping to have something for you all early though. Looks like the viewers have voted for the Youkai Trail. That'll be a fun and laid back trip. Possibly giving us a glimpse at other youkai, and let Mystia and Rumia talk a little before they reach the Human Village. They'll arrive late, and Oscar may be so tired a random event may happen...And some events will have a chance to happen later, like Cirno talking Oscar into helping her waste the Three Fai--I mean visiting the Radio Tower.
Ironically, from what I can tell despite the Magic Forest being described as a very dangerous place, its pretty harmless compared to elsewhere. Sure, it has toxic mushrooms, monsters, youkai etc. But is it really worse than Youkai Mountain? Muenzuka? The Netherworld has ghosts which can kill you just by touch. And there aren't multiple protagonists who live in screaming distance. So, we have options for things going wrong for Oscar, but they won't be so bad...probably.