Probably the resolution should be about 50 ppi, Depends on the viewing distance. You can google for it.
Thanks for the reply! The viewing distance is around 2-5 meters.. It's a backdrop for a booth.
So the resolution or image size is really that large?
also what would be the best format if I will save it as flat image? ( PNG,JPG )
I would avoid jpg unless the data transfer requirements make size a significant factor and go with tiff for example.