>>25208711You'd find more answers on the CYOA thread.
Also, here's an old trick that I used when I used to run horsey time rpg adventures.
Google Welcome to PonyVille Game.
Find the assests
Use digital editing software to copy paste.
????
Profit.
As per specific styles, you may want to try your hand at vector editing itself, and for OC's you'd have to ask individually, and make them into vectors for the adventure. I call this process "Rendering" but in all reality, it's just making the area around the character transparent and making sure when you resize it that it keeps its legibility.
If you follow this advice, I'm sure you'll have a good time!
Cheers!