Help understanding folder permissions

Good day all,

I need some help understanding folder permissions before I really screw something up. 

I got the nextcloud AIO container(s) working and it's so fast and the doc editing works out of the box, no issues... it's great! However, i keep all my docs/media in a separate share incase NC decides to die, i don't have everything in the NC directory. I was using the external storage app on my old instance and it works great. However with the AIO instance, you can only map 1 external path for some reason. I got this working but the problem is that I'd like to map more than 1 external path (dosc, pics, media etc). So the solution on the AIO readme is THIS. I'm very hesitant to add/change the permissions the mnt/users folder as it contains EVERYTHING. 

Since I don't know much about how permissions work, will entering the lines into the console

sudo chown -R 33:0 /mnt/your-drive-mountpoint 

and

sudo chmod -R 750 /mnt/your-drive-mountpoint

overwrite permissions? or just add the 33:0 and 750 permissions to the mnt/user directory? I'd hate to change something and have it all come crashing down. 

In the readme their solution is to mount the mnt/user with the above permissions then, what i would do, is favorite the different folders I want. Is it silly to give NC access to the mnt/user folder as it, again, contains EVERYTHING? Anyone with some NC AIO experience want to share how they tackle this? Thanks!