Yes, 8.0 runs even in Snow Leopard.
Also: look in the Help menu and see if there is a "Deactivate" choice. (I think 8.0 is before that started, actually.) If so, then you should deactivate Photoshop, install the new OS, then activate it again.
Error 50 is a generic - iTunes has failed to write a file and the article listing specific store errors (expand the section on Specific Conditions and Alert Messages to reveal -50 in that section) deals with the usual problems where the store is failing or the network is failing.
If the error is bubbling up from the filesystem (or you get the error from Finder), then it's often an "illegal" character in the file or folder name. Look to remove or rename files with emoji, unicode characters or more mundane characters like : & or /
In your case, it's very likely the drive is the cause. You can and should look in the console app to see what other errors happen around that time. Look for I/O errors - disk0 - or just run disk utility and have it verify / repair the catalog file. This will confirm the guess that the drive is failing and the errors are not some software problem.
You could export the current library xml to the desktop and start over with a brand new iTunes library file just to rule out corruption in that file, but then you would have two problems at the same time - terminal unable to write a file and iTunes unable to write a file. Occam's razor (and my experience) says it's the filesystem/drive - not two identical software problems.
Spinning hard drives do track the sectors where a bad write has happened and try to keep track of them so the system won't notice files not vein written, but as a drive ages (or if this mechanism fails) you will get unrecoverable errors more and more.
Also - it's often hard to tell if the catalog structure is bad (which Disk Warrior, Drive Genius and plain old erase in Disk Utility attempt to fix assuming the drive works properly). But if the underlying hardware is failing, you'll need to move to a new drive.
I would just make another backup and zero the drive and look for errors during the zero / reinstall. If the errors persist, it's time for a new drive once the pain of reboots is more than the cost of a new part costs.
In your specific case of an old PPC machine where repair is invasive and the cables likely to be brittle, I would just re-install the OS onto an inexpensive and many GB external drive and run the mac from a cheap USB drive (most iBooks will boot from USB, but not all will) - leaving the potentially failing internal drive sitting unused, unmounted and spun down. It's rare for a failed drive to take down the machine so you can just leave it alone for minimal cost if you can tolerate the iBook running on an external drive.
Best Answer
What your friend is likely talking about is not connecting it to the Internet as the newest macOS that works on that Mac is OLD.
And that matters because it does not have the benefit of updated patches to macOS that make it more secure and more importantly it runs a badly outdated version of Safari that may not even connect to most modern websites due to standards changes in web publishing and the outdated security certificates built-into old versions of macOS.
Depending on which iBook you have you may be able to install a more modern browser. I have an old G4 tower with some older, never updated, apps on it that I use from time to time and use a version of Firefox called TenFourFox. It (as I have been told) supports G3 and G4 processors. So that particular browser would be safe to use due to its more modern foundations, if slow on modern websites.
I believe there are other, alternative, browsers for legacy versions of macOS, but I have no direct experience with them. Other folks here may be able to chime in and offer suggestions, but it would be good if you edited your original question and add the model of iBook you have and the version of macOS installed on it.
But without a more modern browser I would also suggest you avoid connecting to the Internet, merely for safety reasons. Wi-Fi, itself, is likely okay as long as you are only using it to transfer files between your local Macs and not going out onto the Internet.