For the first time I'd go with an iMac 27 "purchases, because it does involve an expensive investment, it must be aligned correctly. What do I do with this iMac 27 "? The intention is for this iMac especially for light photo-editing (ligthroom) and light video-editing like iMovie, which further converting en encoding many audio and video files (MKV). multitask, everything else is normal usage. How long do you wish to use this iMac? I hope with this investment and 4-5 more years to have fun. Much or little storage space? All my data is externally Nas as a backup safely stored! I wish no mechanical drive and thus have an SSD; How big exactlythis you only need to continue for years to be able to estimate forme difficult. Currently, I am now working for a year with a mac mini i7 2.3GHz 16GB RAM + SSD256GB. Which suits me fine for everyday tasks, only when I output tasks such as rendering video files BD files to MKV and many audio files from FLAC to MP3 or Alac it is too slow to me. Even when converting various raw photos, much of the Mac Mini is requested. Just because I have the iMac to replace the Mac Mini for the coming of years will have just a bit faster. 27-inch iMac with Retina Display 5K Processor: 5i and 7i ??? Memory: 8GB, later expanded to more. SSD: 256GB or 512GB ??? Graphics: ??? Magic Mouse 2 + Numeric wired keyboard.