Apple iMac (Retina 5K, 27-inch, 2017) Serial Number Lookup - AppleSN.info
Apple 27-inch iMac with Retina 5K display (2017) review: All-in
Install memory in an iMac - Apple Support
Install memory in an iMac - Apple Support
Amazon.com: OWC 32GB (2 x 16GB) PC19200 DDR4 2400MHz SO-DIMMs Memory Compatible with Mac Mini (Late 2018), 27" and 21.5" iMac (Mid 2017), and Compatible PCs (OWC2400DDR4S32P) : Everything Else