Texture Designer does not create new 3D models from scratch except Mlo Creator. Texture Designer's services are limited to retexture work and setup of existing models (YTDs).
GTA 5 limitations mean that only one instance of the same 3D model can work if two identical models share the same slot. Compatibility is not guaranteed if duplicates are present.
Clients must provide clear requirements as well as assets for the retexturing process. Lack of details may result in delays or unfulfilled expectations.