All your skins files need to be saved in .dds, dx5 format (can it be for bodywork or windows, or extra files), with a full white alpha channel for textures linked to region files. Detailled rendering will be done using region file.

 The templates are done with a 2048*2048 resolution, howhever feel free to bigger it to 4096*4096 resolution before starting to create paint shemes, so you will have a better resolution for the paint and the sponsors of the cars.