"Would you recommend using Photoshop for designing professional event posters and wall graphics?

start the layout & all the photos(images)  & background in photoshop & bring it to illustrator for the text & logos

Illustrator is your tool, or any vector based application, because it deals with pixels differently, it is better for large scale graphics, especially the ones set up to be printed, the file size generated is smaller and more maintainable 

Of course Photoshop is anything can be done for posters or wall graphics as well advertising but it is depend on a person how he or she can use it the software.