A normal high resolution file from a reasonably current camera will usually work at most sizes. By that I mean sensors in the 24-36 megapixel range. The trick is that the bigger it is, the further away it will be viewed from. For large wall-sized banners you can often have an effective resolution down to 25ppi.
What determines this is the angle of your total field of vision. A piece of paper held in your hand, or a large banner up on a wall, will often occupy the same angle and thus the same "absolute" size visually. Of course some cases will require higher resolution, particularly if the result needs to be seen from close up. In that case you may need to stitch several files.
If you're making "mixed" designs with text and vector elements as well as photographs, you should really use InDesign. Photoshop is not the right tool for that.