Have you considered something already packaged like Nethserver? With that you can install Nextcloud with video conferencing and file management. Nethserver also has support for virtual machines with KVM, meaning you can install whatever additional applications/OSs you like.
We are using Zentyal (http://www.zentyal.org/) at the back-end, and Thunderbird with the Lightening add-on for the client end of things (both Linux and Windows clients). I have to say that I find it very reliable and very functional, although our use case is not really that demanding. I have also been following the rapid development of the Nethserver (http://www.nethserver.org/) project which I feel holds promise as a possible alternative for the future.
As previous commenters have said, it all rather depends upon what you want to use the servers for. That said, I can recommend both Zentyal http://www.zentyal.org/ and Nethserver http://www.nethserver.org/ as candidates for possible drop-in replacement for some windows server installations
If you're a Web guy, you might be more comfortable with Linux, and a setup like this could easily be replaced by a Linux-based offering.
Have you heard of Zentyal or NethServer? There are others in that arena, maybe worth your consideration.
I'd follow the recommendations already made in here about manually configuring Smb4. However, I found yet another all-in-one utility like Zentyal (which works great), which is NethServer: http://www.nethserver.org/
So far, it doesn't seem to be as well put together as Zentyal, but it can be useful. We were thinking of doing a SBS-like product based on one of these distros, but we tend to like to stick to RHEL rather than Debian.