We handle up to 4k res, h264 and we use After Effects as well as 3DMax for some of our video projects.
Up to 8 people could be working simultaneously.
Does the 2640 v4 not have a 3.4 boost frequency while the 2643 v4 has a 3.7 boost, so is the difference that great, or is the boost not available on all cores? Dual chips is the idea for the long run, though buget is an issue for now, and the 2643 v4 is nearly double the price of the 2640 v4.
The server should run nearly 24/7. Downtime at night or on the weekends would be a possibility though, but remote acessibility is a thing that we are considering as well, as to make working from home on the weekends available for our employees.
As for Backups, the projects that are not finished and given to the customer yet will be stored on the server as well as on the IMac working on it. Another copy is supposed to be stored and updated every few weeks on HDDs that will go to a remote site. As soon as a project is finished and delivered the copy on the IMacs should be gone. The copy on the server stays as is, and every half year or year we want to catalogue the projects of the year and put it on remote HDDs named after the year and have a safekeeping in that way.