Music/iTunes App Broken? Should I return my iMac??

I recently received an iMac as a very expensive Christmas gift from my spouse. I was very excited at first, but I am honestly already tired of struggling with iTunes or the new Music app or whatever Apple wants to call it now...

I have maintained a large library in iTunes for more than a decade on two older Windows PCs, and I thought that an iMac would make this a more seamless experience, because both are Apple products: hardware and software. But days later, I am still unable to successfully transfer my music files, playlists, album artwork, in perfect harmony.

I first tried to use an external drive, but several thousand files ended up missing from iTunes after dragging and dropping. And then it looks like the album artwork and other metadata are missing.

Then, an online chat rep suggested I use Home Sharing to transfer between my old PC and my new iMac. But that quit somewhere in the B’s which was more than 10,000 files short of what I was trying to transfer. I don’t think wi-fi can ever be a reliable medium within which to do such a large-scale transfer of files.

So my question really becomes, was purchasing an iMac for the sole reason of having my music in one place on an Apple product a good idea? Or have we spent a few thousand dollars on a glorified paperweight: one that is quite user unfriendly and an uphill battle to run smoothly?

My iPhone has not had anywhere near as frustrating as a learning curve as this computer. And quite frankly I do not think I have the time or patience to force what I think should be a seamless integration. I just want to map my iTunes layout from my old Windows 7 PC identically to iMac Big Sur. Is this too complicated?