I guess the answer is "it depends".

If you want to use the most common functionality and options, then yes - Webmin should provide the necessary options.

However, there might be some advanced features and edge cases that's not covered by Webmin, but I'm not aware of what these might be exactly.

The Samba module wiki page explains what settings you can expect to find in Webmin Samba module.

This is so strange to me that I'm commenting just to keep track of how this gets resolved.

You've set up 3 external HDDs via USB as a logical volume?

Just for my information, what commands did you use to do that?

How did you set up the logical volume?

What is the output of lvdisplay,pvdisplay & vgdisplay?

I agree with u/Max-Normal-88 that you should not mount things under /etc. That's why there is a /mnt, for mountpoints.

/etc is really only supposed to root accessible, not shared.

So, perhaps create a folder called /mnt/Storage and mount the logical volume at that mountpoint.

Also, the mountpoint should be /mnt/Storage, not /mnt/Storage/Directory. After the logical volume is mounted, then you can create /mnt/Storage/Directory. Until it is mounted at /mnt/Storage, if you create /mnt/Storage/Directory, the sub-folder Directory will be created on your local drive, not on the Samba logical volume.

I don't know how to create users and passwords using webmin. I have always done it using the command line.

But usually, the user must already exist as a Linux user in /etc/passwd. (I could be wrong here but I've always done it like this and it works for me)

Then, I would create the user with

smbpasswd -a <username>

Again, I could be totally wrong here, but the internet will correct me. The internet hates people being wrong :)

Now, does one find a Samba server?

Samba, if I remember correctly, has an election(?) which announces a master(?)

https://www.linuxtopia.org/online_books/network_administration_guides/using_samba_book/ch05_01_03.html

So, one of the Samba server(s) on the network needs to become the master browser(?)

I normally run nmap to find stuff on my networks.

10:55 AM:root@tpad:~# nmap 192.168.10.111

Starting Nmap 7.12 ( https://nmap.org ) at 2020-07-27 11:04 AST
Nmap scan report for sme (192.168.10.111)
Host is up (0.00021s latency).
Not shown: 985 closed ports
PORT     STATE SERVICE
21/tcp   open  ftp
22/tcp   open  ssh
25/tcp   open  smtp
53/tcp   open  domain
80/tcp   open  http
110/tcp  open  pop3
139/tcp  open  netbios-ssn
389/tcp  open  ldap
443/tcp  open  https
465/tcp  open  smtps
515/tcp  open  printer
636/tcp  open  ldapssl
993/tcp  open  imaps
995/tcp  open  pop3s
3128/tcp open  squid-http
MAC Address: 00:19:66:FC:89:FB (Asiarock Technology Limited)

Nmap done: 1 IP address (1 host up) scanned in 0.56 seconds
11:04 AM:root@tpad:~# smbclient -L //192.168.10.111
Enter HOME\root's password: 
Anonymous login successful
OS=[Unix] Server=[Samba 3.6.23-53.el6_10]

	Sharename       Type      Comment
	---------       ----      -------
	print$          Disk      Printer drivers
	Primary         Disk      Primary i-bay
	bunch           Disk      a bunch of files
	movies          Disk      movies
	music           Disk      music
	pix             Disk      pictures
	IPC$            IPC       IPC Service (SME Server)
Anonymous login successful
OS=[Unix] Server=[Samba 3.6.23-53.el6_10]

	Server               Comment
	---------            -------

	Workgroup            Master
	---------            -------
	HOME                 SME
	MYGROUP              PENTIUM
	WORKGROUP            LINUX
11:05 AM:root@tpad:~#

Once the nmap scan shows port 139 open, I know that's a Samba server(?)

Then, I can try to connect with smbclient -L //<ip-address-of-Samba-server> to get a list of shares.

I don't if this helps.