There may a simple answer to my question but I don’t have the technical expertise to figure it out for myself. Is there a way of me to purchase music online and to then have it download directly to the internal drive of my Nucleus?
I haven’t had any luck searching for an answer on the forum but I may not be using the correct search terms.
Yea, the nucleus has a drive which you can map over a network.
Just use that as a save location for the music on your Pc
Do you have an additional internal Drive in your Nucleus?
Usually not standard, but you can mount an extra 2.5" SATA disk inside the Nucleus. Nucleus with either 2 or 4TB SATA SSD disk mounted from factory exist.
No. Not “automatically”.
Depending on where you’re purchasing from and how the purchase is distributed to you you’ll need to copy over the individual files to the Nucleus using the guidance others provided above. Additionally, a lot of us have a specific structure to the directories…
Some use genre (jazz/artist/album)
Some just use artist/album or artist_album
Roon does not care how you organize your music except for box sets and then there is some specific guidance to be followed in order for that to work properly.
I did install an SSD when I bought the Nucleus.
Are you saying that I would need to install a second SSD inside of my Nucleus?
Thanks, I’ll spend some time reading this link and hopefully, I’ll understand it.
I use the Qobuz desktop app. I purchase from there and I can specify the music storage location. I point it at roon.
Qobuz automatically downloads new purchases when I have the app open and they are added to my collection fairly transparently.
Frankly, I would not download purchased music directly into a Nucleus (or any folder watched by Roon), but always use a staging folder to collect the downloaded album(s) first before copying them across to the Nucleus. That’s best practice, similar to ripping CDs.
Over a network, many file copies are no quicker than a fast download. Roon still ends up seeing files that are gradually added. Downloading direct and transferring over network is no different imho.
Yes, if you don’t have a disk installed (not thinking of the Roon OS/Database SSD), you can install an additional one (either mechanical or SSD) SATA 2.5" drive into the Nucleus. Post installation you need to enter web UI for the Nucleus and format it.
I have 2 Roon configurations (2 different locations). Nucleus+ in one, and Intel NUC8i7 in the other. I installed a Samsung 870 SSD 8TB in both. Works like magic 
I did install a 2.5" SSD in my Nucleus when I first purchased it. Are you saying that an additional SSD would fit inside my Nucleus for that purpose?
Why would it be a bad idea to download them directly onto the SSD that I installed into my Nucleus?
I just like a belt and braces approach of using staging folders. Feel free to disagree.
Oh, I don’t know enough to have an opinion, I’m just trying to educate myself.
What are belts and braces? Nevermind, I just Googled it. 
No, you can only install 1x2.5" SATA drive. Roon OS and database are stored on M.2 SSD.
Edit:
But if you already got a SSD SATA drive mounted in your Nucleus, this is where you copy your purchased music. You can create a separate folder if you have FLAC files ripped from CD (or downloaded in other ways).
Does the Nucleus have AV software running ?
I have a 4Tb HDD for music, AV software , depending on which one, scans on and off the drive so slowing down reads. This can cause problems, it certainly does with JRiver. I run Windows Defender on Windows 10.
My main library drive is excluded from AV for that reason. So any new files come into a (staging) drive scanned by AV and should there be a problem it’s spotted and fixed before being copied to my unprotected drive.
Works for me. If you want more info go to the JRiver forum there is a thread “Taming Windows Defender “
I have no idea if it does or even what that means. 