Basic Questions About Local File Storage in OS Catalina

Folks, please be patient with me. I have 30+ years' experience working on computers, including 12 years on an iMac (OS Snow Leopard) and when I bought my current computer, MacBook Pro, OS Catalina 10.15.7, I read the MacBook user's manual and also the OS Catalina manual. All that said, I am still unsure about some very elementary matters about data file management on my new MacBook.

1. If I want to store data files on the hard drive of the MacBook, I can open Finder, open Macintosh HD, open the Users folder, then open my own user account (let's call it "Jonah") and create folders to store data files locally. Correct?
2. If I download data files into MacintoshHD>Users>Jonah>Downloads (i.e., the downloads folder that exists in the "original factory settings" in Catalina), then those data files are stored on the hard drive in my MacBook Pro, right? So when I use Time Machine to back up files to an external hard drive, they get backed up and are available to be restored if the data on the hard drive in my MacBook Pro is lost, right?
3. I am (successfully!) using iCloud to sync photos between my iPhone, iPad and MacBook Pro. When I bought the MacBook Pro, I had to manually transfer all my photos from my old iMac. After doing so, in Finder, it appears that the photo files are stored locally in MacintoshHD>Users>Jonah>Pictures>Photo Library. Do I understand that correctly? The files are not simply on iCloud with no local file storage?
4. I am (also successfully!) using iCloud to sync my various document files (.pdf, .doc, .docx) with my iPhone and iPad and MacBook Pro. Because I had to transfer my files manually from my old iMac, and because I didn't know what I was doing, I put all my document files on a USB drive and copied them all into a folder that was already on my MacBook Pro, called "Documents." Now that I am getting to know my MacBook better, I see that this "Documents" folder is listed under a small-print sub-title that says "iCloud." So the files in this Documents folder are not on the hard drive on my MacBook Pro? When I use Time Machine to back up onto an external hard drive, I am not making local back up copies of my document files?
5. I had to manually transfer my old iTunes files (200 CDs, ripped by me and uploaded onto my old iMac). It seems that they are in this location: MacintoshHD>Users>Jonah>Music>iTunes>iTunes Music>Music. So those files are on the hard drive on my MacBook Pro? And when I use Time Machine to back up onto an external hard drive, I am making local back up copies?

Thanks in advance for helping me re-learn the basics of file management in the age of Catalina and the iCloud.