Inital concerns about Setup

Please some help and advice.
After returning home after many years living abroad where the internet was slow it's great to be in a country where I can use Plex and get my media files connected up throughout my new home. However, before creating my setup I need some advice and guidance in obtaining my desired results.
At the moment I have my music on my Macbook using iTunes. My wife has hers on her windows laptop using WMP. My daughters movies (with an array of different media file formats) are on an external drive which is formatted to FAT32. My first concern is, would I be able to transfer all of these different files onto a NAS system from different sources? There will be a total of 4TB of files. Any advice will be gratefully received plus any suggestions as to what would be the best NAS to buy?
Hopefully if my initial concern can be overcome and everything has been successfully placed on the NAS, I will then put Plex apps onto the various TV's situated around the house. For music I will connect several Chrome Audio devices around the house, kitchen etc. connected to stereos. I will be using the Plex app on my iPhone to cast to the Chrome Audio devices. Would this be possible to do or would there be complications?
Any advice will be most helpful. Thank you.