My wall has a really rough texture. Will that affect the painting?
I can paint on a rough texture surface, but it does affect the artwork. In many situations the texture can enhance the artwork; a rough surface allows for interesting textures and layering. If the mural will be viewed up close, and has a high level of linear details (for example, trompe l'oeil style murals), you might consider either re-plastering the wall or having the mural painted on panels.
Here are two examples of high detail murals painted on rough surfaces: