It is answered in the LFS Editor FAQ: https://en.lfsmanual.net/wiki/LFS_Editor/FAQ#Skin_ID_is_not_suitable_for_upload_-_you_need_a_Skin_ID_from_LFS.net

It’s also mentioned in 3. of vehicle mod regulations, which I recommend reading: https://www.lfs.net/files/vehmods/regulations

Mod submission guide: https://en.lfsmanual.net/wiki/Vehicle_Mod_Submission

LFS Editor on LFS Manual: https://en.lfsmanual.net/wiki/LFS_Editor

No, user data will not be overwritten.

You can use google or another search engine and type “LFS 0.7E12” and find it too

Mandula effect

Shift - (minus) toggles all in-game messages off

Also check the Skins tab on the mod detail page if it has some templates. For example: https://www.lfs.net/files/vehmods/D289BE?skins

Did you take the engine sound file from my Karobus mod?