Hi, im new to the forums (though i have been reading posts on these forums for many months) today i pre ordered this game and i was wondering will there be an interior car designer? Sorry if this has already been posted 
No. there will be no interior designer. But you can select the number of seats and various safety and luxury option (airbags, cruise control ect.).
This will show you how the interiors are working at the moment… Its a few minutes in after the engine is built.