Macintosh HD space clearing question - External TimeMachine setup questions

[landshark2]

My ultimate goal is setting up my external HD as TimeMachine for Mini, MBP and iPhone, but I now see an exorbitant amount of data in the Mini's Documents. When I look at Documents via Finder, there aren't any such large files, so I'm assuming Downloads are included in that Storage number. Yes, there are many photos and videos in Downloads, which I need to relocate or delete.

First question is about what I'm assuming are failed or incomplete AirDrops, with Zero Bytes. All but the most recent long iPhone video have corresponding successful uploads, but when I attempt to move any of the Zero Bytes files to the trash, a warning popup says the file is in use by another app, and that trashing the file could cause problems with the app using the file. Am I correct to assume that AirDrop will be okay if I trash all these Zero Byte files?

Second question is about partitioning my 1TB external drive, which currently only hosts my Music folder. It appeared that I was creating three 333GB partitions, but it ended up creating two 250's and one 500, with the Music folder partition, the one which retained the MiniDock name, being one of the 250's. Continuing with my assumptions, going back to DiskUtility and increasing that one's size to 500, and downsizing Untitled2 to 250 should be easy peasy, right?

Third question is about the fact that I don't need to backup the Music folder on either the iPhone or MBP, because that folder exists in full on the external MiniDock drive, so how do I set up TimeMachine on the external drive to not backup the music folders on the iPhone and MBP?

 

[ChrisA]

Why did you create partitions on the drive? Maybe because you wanted to create a hard limit to the amount of space a certain set of files can take?

You might want to back up those files. The best backup plan is to always have the data on three physical media and at two different geographic locations.

How to exclude files from TM? open TM settings --> Options -- > navigate the drive/folder to be excluded, click OK.

The external TM drive needs to be much larger, perhaps 2X the size of all the data you want to back up as it will hold old versions of al you files. I'd say at least 1.5X and, of course, APFS.

 

[landshark2]

I partitioned because the first time I tried to install TM a full wipe was required, and I wasn't willing to wipe the music folder.

I envision about 300GB max storage of Music, photo and video on external drive. All of the Music and much of photo and video would also be on the MBP, and the Mini would have a significant photo and video overlap, without any Music.

As I see it, considering the 4 devices innate overlaps, I can severely constrain necessary TM backup space, can't I?