Copying various selections of images from my Photos library to a new library

You can do what you want all in a single library.

1 - assemble the vacation's photos in a smart or normal album named Vacation - 2024.

2 - mark those favorites with the Favorites icon in Photos:

2 - create a smart album with these criteria:

3 - and you'll get this:

That will get you only those photos in the Vacation - 2024 album that have been marked Favorites. You do not have to increase storage size as albums are virtual entities requiring no additional space on the drive.

On a Mac, you can have more than one Library. I have a bunch. But only the System Library can connect to iCloud and synchronize with your other devices.

I have several Libraries with old family pictures, and such, that I'm through editing and don't get changed much. I have a Favorites library with pictures that I want to show friends and family, and which I'm happy to look at, myself. I can keep other Libraries on external drives so they are available but don't take up room on my internal drive.

I try not to keep too many pictures in an Album. Albums can go in folders, and folders can go in folders, so most albums have less than 50 favorites, maybe one for each day or two of a trip, all in a folder for that trip. All the trips might go in a folder to the season, Fall 2015, maybe. I have folders for years and, since I've been doing this awhile, I have folders for decades. It makes it all way easier to scan to what I want without going through 500 albums.

I use Smart Albums for some recent events, since I might change what I think is a favorite.

Pictures aren't exactly "in" an album. When you put a picture into an album, its name is added to a list of pictures to display together when the album is clicked, kind of like a music playlist, but for pictures. So two albums can both have the same picture name in their lists, and that picture will show up when you click either album--but there's only one picture file-- it's just on multiple lists. And when you remove a picture from an album, its name remains in the lists of other albums, and the file still remains in your Library. 

So albums give a specific view of your pictures. The picture of "Aunt Ethel at the Grand Canyon" can be in the "Aunt Ethel" album with other pictures of Aunt Ethel, and it can also be in the "Grand Canyon"  album with pictures of other people at the Grand Canyon. And it can be in a the "September 2015" album, too. Each album is pointing to a single file stored in the Photos Library, so having pictures in multiple albums takes up no more storage space. As you can imagine, this is very powerful in organizing pictures. I don't have to remember if I put the picture with Aunt Ethel at the Grand Canyon or with the other Aunt Ethel pictures-- I'll find her in either.

This is what I do, and others do similar and different things. If you need details, let us know...

Richard and Old Toad have already given you good advice.

It helps to plan in advance, how you want to use Photos, and then to design your Photos Libraries according to your needs.

The number of Photos Libraries you are setting up will be a trade-off between the convenience of having all photos you need together in one library and your patience, when Photos is getting slow when it needs to upgrade a Photos Library to a system version.

The library size matters most, when Photos needs to scan the library and analyse it for objects, scanned, and faces, but also searching it or defining many smart albums, or when we want to make backup copies of the library, so we would want to keep the library sizes small. On the other hand, all related photos, that we would need together in the same Photos Library, when we want to create slideshows or other projects, should be in the same library.

Like Richard, I am keeping all favourites in the same library and in iCloud Photos, and a collection of all my photos in separate, small Photos Libraries, one library for each major photo safari, and one for each year.

This user tip might give you more ideas, what to consider, when you want to design your system photos library: New to Photos? Some Considerations on How To Design your First Photos Library- Apple Community

Power Photos is a great companion for Photos, particularly when working with more than one library. We can have more than one window and compare several albums within the same Photos Library, or compare albums from different Photos Libraries, merge libraries or copy albums or folders between libraries. We can even import albums directly from our iCloud Photos Library into other archive libraries.

Richard.Taylor wrote:

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That is to divide a single Library into two, a personal part and a shared part. Only the shared part goes to iCloud. This avoids having the Favorites being an additional copy, taking up more space. So you should look into this:

How to use iCloud Shared Photo Library - Apple Support

You may have misunderstood how the "Shared" iCloud Photos Library is working, Richard.

When we are setting up the Shared iCloud Photos Photos Library, our iCloud Photos Library will be split into two compartments, a personal library and a shared library. Both Libraries will remain in iCloud Photos, but we can invite other people to share our Shared iCloud Photos Library. we share photos by moving them within our iCloud Photos Library from the personal library section to the Shared Library section. There is a nice toggle switch that lets us view both libraries together or only one of them. I am keeping my most important photos that I want to show to others in the Shared iCloud Photos Library, but without sharing them with anybody but myself.

Well, first, you need the 3rd party app PowerPhotos ($30). This has been a trusted app for use with Photos since the iPhoto days 20 years ago. (There have been many apps that really mess up a Photos Library, so beware!) PowerPhotos makes it way easier to manage multiple libraries and to copy pictures and albums between them. I keep PowerPhotos open on my Mac anytime I have Photos open. Really, pretty much anyone who uses Photos much has this app.

The System Library is the one that is automatically used by other apps, like Safari or Screensaver, etc. If you drag a picture to the Photos icon, it goes into the System Library. There is only one System Library, and it's designated in Settings>General, like this:

"Use as System Photos Library" is grayed out, here, because this one already is. Unlike iPhones and iPads, Macs can have other Libraries, but only one System Library, and that's the only one that can connect to iCloud on a Mac.

If you turn on iCloud in Settings>iCloud, then all the pictures in this System Library are copied to the iCloud Photos Library. Also all the pictures (except duplicates) from iCloud are copied to the Mac. Photos will make both the Mac System Library and iCloud Photos Library have exactly the same pictures. The same happens if you turn on iCloud in the Photos Settings on an iPhone or iPad. They will all have the same pictures.

Each device needs enough room to handle it all. On my iPhone and iPad I choose "Optimize Storage" so that the mobile devices keep only smaller images. When zooming in or editing, the full picture is automatically pulled from iCloud. On my Mac I choose "Download Original Photos" so that I always have the full sized images available for backup. On your Mac mini, you may want to move your Library to a fast external drive, SSD is best. See this:

Move your Photos library to save space on your Mac - Apple Support

Pay special attention to formatting the drive-- An SSD should be formatted in Apple's APFS.

I think the way I started was to duplicate my Library and name it something descriptive. Then, on the original, System Library, I started deleting things I didn't consider Favorites. When you delete a picture, it's deleted on iCloud, on your iPad, everywhere, since it's all synchronized. Every picture in the Favorites Library is a copy of a picture somewhere else, so I don't mind messing with it and deleting things. You would want to get most of this done before connecting to iCloud, so iCloud won't be constantly copying and erasing maybe thousands of pictures.

New pictures from my iPhone are added to the iPhone's Library and are automatically copied to iCloud and to my Mac. Then I copy the new pictures to an archival Library, and I delete the less interesting ones from the Favorites Library.

There is a completely different way to go that I don't use, mostly because I'm too lazy to try it. That is to divide a single Library into two, a personal part and a shared part. Only the shared part goes to iCloud. This avoids having the Favorites being an additional copy, taking up more space. So you should look into this:

How to use iCloud Shared Photo Library - Apple Support

I would have wished it were as you have described it - a really separate shared library, independent of our own iCloud Photos Library. The way Apple is advertising the Shared Library is suggesting a separate second library.

Maybe I should have read about it more before I talked about it (blush!) Of course the whole Library is in iCloud Photos.