We moved partially away from Apple Server about 15 months ago and are still transitioning some stuff.
for DNS: as per Karl, use your router you can, but bear in mind that if you want AD, your AD device will insist on being the DNS. Consider using secure DNS services such as OpenDNS or AdGuardDNS in order to reduce risk of malware to internal devices.
for File Storage: Don’t use external Cloud services if your users work on large files (e.g. video or PowerPoint/Keynote with lots of images and graphics), unless you have a VERY fat bandwidth pipe e.g. >250Mbit/s uplink speed. If you are only storing standard Office files, then you can get away with Cloud storage if your uplink speeds are >20Mbit/s for a small number of users. Bandwidth restrictions also cause problems with database applications where the server is off-site (e.g. Access, FileMaker). For a solid on-site file store, Synology is great, otherwise QNAP or similar NAS work well.
Mail: Use your ISPs own IMAP service, unless you have a large number of internal users.
Other Groupware: Synology have these built in as do most of the other linux-derived NAS products.
Authentication: If you need hot-desking, you are going to need help. Macs authenticate nicely (e.g. Bind) with Active Directory (either Microsoft or Synology), but getting home folders working correctly is a real pain (I’m still trying). Basically, Apple deprecated and removed some of the Network Home functionality from the Mac Client, so be prepared for a challenge if you need users to jump from one machine to another and have their home directory files (which includes Mail BTW) move with them.
Printers - we are currently manually configuring these to provide notifications to our ICT email address (OKI devices), but otherwise use the printers own built-in print servers.
Profile Manager: I’m still not sure what to do here and looking at all the options that Karl lists. I run a small charity here with very limited IT budgets, so cost can be a major implication. It would be nice if someone could do a summary/review of the various MDMs as to pros/cons of each.
Again, I agree with Karl – keep things simple. We are now reaching the point where IT is becoming a bottleneck in the work we do. Not necessarily because it is overly complex, but because it needs a lot of work to get data in the right form. If we had started doing it from the start, it would be simpler. I am now trying to capture information that should be easy, but is still held on manual paper or spreadsheet records, but transitioning to a database-centric solution is proving to be very much hard to implement as I am constantly playing catchup.