Not sure about it, there a few things on Illusion's paradise mod that i don't really like. For instance, darker asphalt on intersections and other things. I might leave that open, so, people who likes can add them, people who doesn't, don't have to bother going back to original.
Totally right. Every added vehicle will be shown and editable in TDU PE and Modding Tools.
And as said before Stories, i am looking into many websites, picking newer versions or versions that are correct. I test each one of them and if i don't think it's good enough, it's not in. Another point you're missing a bit though Stories, is that not everyone knows how to put a mod in TDU. And most people know how to, but they don't know how to fix rim sizes.
Example:
This is an image from TDU ReincarNation, or something like that. That can happen to any mod, because it's an inchoerence between the rim size in the rims.db and the Default Rims you choose in TDU PE. So far, none of the cars i've added have such problem, mostly because i had to work a way around, because when you simply add a car over another, it might get smaller than tires or bigger than tires. Common issue.
There is also the problem with tuning packs, TDU tuning shops have a brand limit, i can't put more than 8 or 9 brands in one tuning shop, if i do, it simply won't work and the car won't be tuned.
Another point is, correct color names, with custom cars, most people will be stuck with "Yellow" "White" and so on, they won't have a Rio Yellow Pearl on NSX, or a Verde Germoglio on a Dino. That is why i think it's better to have more actual cars than simply generic open slots. Avoids trouble for most people who don't really know how to put a mod. :D