So, I’m not sure if here is the best place to discuss this, but some effort was already done to make an “enemy mod” for Vesperia.
Looking at what you said, it seems you were working with the party pointers. These pointers can be a good start, but you would need to look deeply at the information that they reference. Pretty much, as you said, they define things like models, stats, levels, and other things.
As Vesperia has 9 characters, anything after that seems like junk (what it looks like from your experience). This is because the developers did not make the enemies and characters have the same format (or follow the same standard). Character 10 will then load junk, which may result in a crash or a random player character with crazy stats. Only games that have the same standard for enemies and player characters will allow this (such as Symphonia DotNW IIRC, since it has an enemy capture feature).
Since you said that you found “Brave Vesperia” and “Dhaos Laser”, it means that the artes do follow a standard format. This is true for most of the Tales series, since some spells and artes can be used by both players and enemies. Keep in mind that normals and other special attacks may not be here, since they may be part of enemy-specific data.
For Tales of Vesperia, it seems like you would need to do things separately (similar to Tales of the Abyss, which I took a look into back in the day, and most modern Tales of games). First, since this is a 3D game, you can have a look at skeletons and characters’ meshes/textures. This is the part where there was some work into it already. You can find some more info here https://github.com/Sora3100/Tales_of_Cheat_Tables/blob/master/Vesperia.CT (from aanpsx – fearlessrevolution). It’s a cheat engine table.
After that, you can probably look into artes. Since you found enemy artes by changing a character pointer, it probably means they are in the same table. You would then change the pointer for an arte shortcut you know (from the artes menu) until you find an enemy’s arte. Hopefully, you find their artes here, since some Tales games only have Mystic Artes in the same table, thus you would have use a pointer to somewhere else.
There are also things like sounds, normal attacks, and basic animations, which you might have to change depending on what a character needs to work (again, you can kinda figure it out by looking at how the character pointer works – the one you changed to 21 and got no crashes).
Your best bet would be looking into how this is done for other games. I suggest you start by looking into Frubam’s experience with Berseria and how his table works (look for “Berseria: Model Code” on Youtube). Really awesome stuff.
Are you knowledgeable about Cheat Engine? They have a good tutorial on the application itself that can get started. With just CE you can do a lot of stuff. After that, you can take a look at how the file system in Tales of Vesperia works (which you can do by “educated guesses” if you only know how to use CE). If things look too complicated, or you start having to change 10s or 100s of values just to fix an error, you might have to just make a script for it (assembly or lua). They can be quite easy to learn depending on how much you know of programming. If you’re new, it might be best to just ask for help or takes things slowly so you don’t burn yourself out.
Edit: Also found this: Tales of Vesperia Definitive Edition (Steam) - Page 54 - FearLess Cheat Engine, may help you out.