File types

[Struggleton!]

OBJ and DAE for model formats
PNG for image formats

And FBX and SMD for models, too, but those are optional.

Along with that you also have to provide an image and an icon showing the model correct.
If so what file type/size does that have to be?
(I also ask because I have models to submit but because I can't apply the textures properly, but others can easily, I cannot upload my models yet. )

Not necessarily; you don't need to provide a preview image. However if you do provide one, it has to be 750x650 for the large icon, 148x125 for the small icon.