Good Morning Robin,
Unless you are a professional wedding, or event photographer, with expert image management skills then working with multiple Adobe Photoshop Lightroom Classic Catalogs is not advised. See One Lightroom Catalog Is All You Need for my long and very dull lecture on why I urge you and 99% of all Lightroom Classic users to work with one Catalog only.
Consolidating all of your existing Catalogs will not change anything about the way that Lightroom Classic imports your images. The same question about copying your new images from the memory card to a specific storage location on hard drive X remains no matter how many Catalogs you use.
But consolidating them all into one will solve numerous other potential problems and it will make it far easier for you to back everything up.
Dishing out vague advice on Adobe Photoshop Lightroom Classic best practices though is easy. What’s much harder, without being able to see into your computer, is giving accurate advice on how best to consolidate those Catalogs together.
One option if you are working with Catalogs that do not overlap, and if you have not extensively used features like the Pick / Reject Flags, Virtual Copies, and Collections is simply to import all of the images from Catalog A into Catalog B as if they were just any other folder of images that you found inside of your computer.
Option two, if there is a lot of overlap or if you used any of the features that cannot be stored as Metadata, is to use Lightroom Classic’s dangerous Import from Catalog command.
Both options have risks and rewards.
If I were in your shoes, and if all of your Catalogs contain important work that you could lose, then I would ask someone like @FoChap to take a remote look inside your machine and help you come up with a clear game plan before you start the merger.
I hope this helps and no matter what you do I urge you to back everything up before you begin merging Catalogs together.