Suggest me a file server for a small business.

I am running a small design studio with ten iMacs and two Mac Mini , Right now I am using local mac to mac share for file sharing and using external HDD for saving the design files and assets.

I would like to set up a dedicated file server for sharing and saving all my assets related to projects. Where I should be able to search and access any files (photos, psd, fonts. etc) from any mac machine within the network using spotlight search locally. These files will be added day by day and I need a regular backup of all the files in case if any system failure happens. Can someone recommend me the best possible solution for this.

Thanks in advance.