"The above iTunes download link resulted in an error"
What was the error message?
I find Microsoft's decisions to end support and updates for Windows XP confusing"
This is hardly the place to discuss Microsoft's support policy but each edition of Windows has a defined end-of-life date. In the case of XP we're talking about a product that is five generations old - to continue support for XP would cost money and dilute resources available to support more recent OSs.
"We do not want to have to pay high money for a new PC when the PC that we have is fully workable computer."
As previously noted, a PC that's more than 8 years old is increasingly susceptible to serious hardware failures. New PCs meeting your needs don't cost a lot - neither my primary home system (Dell micro desktop) or my personal laptop (HP Stream 13) cost much more than $200.
"I wanted to download iTunes and Apple Music for listening to music."
While there are alternatives to iTunes as generic music players, I'm not aware of any that support Apple Music. Apple Music requires iTunes 12.2 or later which in turn require Windows 7 or later.
"Windows 10 users are reporting serious problems with Apple's products"
Personally I've had no issues with iTunes on Windows 10, or heard of any encountered by family members / friends / co-workers, and based on evidence from here and elsewhere I've no reason to think that users encounter more issues with Windows 10 than they have with previous editions of Windows.