xsrv VS OpenMediaVault

Yes, OpenLDAP installed from this ansible role

It's dead easy to use TCP/SSL instead of UDP to forward logs. Example rsyslog config

I use rsyslog for that since it's the default in Debian. Configuring forwarding is very simple, a single file in /etc/rsyslog.d/forwarding.conf [1]. Note that this setup uses TLS to encrypt messages so you need to create the relevant certificates (I use self-signed certs). Unencrypted TCP or UDP is simpler, but less secure.

preseed.cfg contains a few basic options needed to setup the OS [1]

I do this with https://github.com/nodiscc/xsrv/tree/master/roles/openldap + https://github.com/nodiscc/xsrv/tree/master/roles/samba. It's just a standalone samba server + LDAP auth for users, no DC or anything like that, so I'm not sure this is what you're looking for.

This ansible role (check the tasks/ directory) gives a good breakdown of what is needed to setup a basic LDAP server and authentication service

I use samba in standalone mode with or without LDAP auth https://github.com/nodiscc/xsrv/tree/master/roles/samba

You might want to consider the previously mentioned MergerFS and SnapRAID, or MDADM and LVM for your setup. OpenMediaVault [https://www.openmediavault.org/ is a solid choice in this regard. Additionally, if you're planning to run something like Proxmox, you could look into deploying Starwind CVM on top of it. Pretty much like in this guide: https://www.starwindsoftware.com/resource-library/starwind-virtual-san-vsan-configuration-guide-for-proxmox-vsan-deployed-as-a-controller-virtual-machine-cvm/ .

You would better to install OMV instead. It's a ready to use fileserver solution with web interface.

So I'm working on a similar setup with an ancient desktop my in-laws were getting rid of. I installed OpenMediaVault directly to the hard drive (it's so old that I assume it wouldn't work too well as a hypervisor), with a 4TB external HDD attached. OMV supports Docker by means of a plug-in and I'm running a Jellyfin container with no issues at all. I'm still manually downloading everything to the HDD but *arr containers are my next step, as well as setting up a gluetun container to route all that through a VPN.

That is possible (it's automated to a certain extent). It also depends on the NAS OS. Unraid, for example, can work with drives of different sizes while using the largest one for parity. TrueNAS uses ZFS so you won't be able to just add a drive to your RAIDZ and expand it. There's also openmediavault: https://www.openmediavault.org/ that uses Linux Software RAID and you can add a new drive there but you can't combine drives of different sizes. And there's also Starwinds NAS that supports both Linux Software RAID and ZFS: https://www.starwindsoftware.com/san-and-nas. Plus, I would avoid SMR drives in RAID: https://nascompares.com/answer/list-of-wd-cmr-and-smr-hard-drives-hdd/

I'd put it like that: if you have a spare PC, then it's definitely worth trying. I would also look into openmediavault (minimal RAM needs): https://www.openmediavault.org/ and Starwinds NAS (supports both ZFS and Linux software RAID): https://www.starwindsoftware.com/san-and-nas