Since you already have the NUC, using it makes sense.
If you were starting from scratch, I'd suggest using an RPi4B as the server platform. You could set up NFS and/or Samba (SMB) servers in Raspbian or you could install a Synology-like solution such as Open Media Vault on it. You could even go to DietPi as the basis for one of their packaged servers (including Emby, Kodi, LMS, Plex, ReadyMedia/miniDLNA, etc.).
I'd recommend you get your feet wet playing with various server solutions with just a few albums first. That way you can separate the server-management issues from any file-management issues. At various times, I've set up NFS, Samba, OMV, LMS, and ReadyMedia services in various Linuxes. It's easy peasy once you get the hang of it, but the first time through it feels like you're tripping over every little gotcha.
For some time my main server has been OpenMediaVault installed on an Odroid HC1 with an SATA SSD [1]. It has been as solid as a rock; never goes down as long as it has power.
Regarding rclone, a year ago after seeing another user's post (
API connection to cloud...), I played with using rclone to mount my Google drive and also my Dropbox directory as a local directory on one of my local players.
I see from some of my private postings to Tim and the test team that I thought the experiment went well but candidly I didn't take good notes and I don't remember some details. I dropped the ball when I went off on an extended vacation and had other problems to deal with when I got back. Tim has been kind and not ragged me about not following up
One critical step is to register through your Google account in order to get a Google Authentication token to plug into rclone so you get good performance. If, instead, you accept the default "client id" you get an authentication token that's shared with every rclone user who accepts the default "client id". This has performance implications because Google imposes rate limits per token.
So now that your post has reminded me of unfinished business, an rclone mount is back on my TODO list too.
Regards,
Kent
[1] I did this before the RPi4B was released. Now the choice seems like 6 or one or a half dozen of the other. The costs are similar. The HC1 is better packaged. The performance of the SATA SSD isn't that much better than the performance of a USB3 drive. The improved networking subsystem in the RPi4B puts it on more or less equal footing with the Odroid HC1. There's a far greater selection of software and much better support for the RPi.