We use Samba4 in the Fileserver appliance; but we use the older config model for simplicity (more for a simple stand alone fileserver rather than a domain member type arrangement). We hope to update that in the future to allow users to easily choose a base config for either standalone or domain usage. We are not anywhere near that just yet though... Perhaps you can help?

Samba4 actually supports using it's own implementation of LDAP although I'm not sure whether that would be the best way to go in this instance. I'm no Samba expert (nor do a I use Windows much these days either) but I did a quick google and found a few pages that may be worth deeper inspection?

Have a look at these for starters (not necessarily recommending them; just from a quick glance they look like they might be useful).

https://wiki.samba.org/index.php/Samba_%26_LDAP

https://help.ubuntu.com/lts/serverguide/samba-ldap.html

TurnKey is Debian under the hood (v14.x = Jessie) but Ubuntu is pretty close...

If you document your steps then you could post progress notes and help us develop a better fileserver! Keep us posted on how you go regardless! :)