Your copy of Windows is locked to the PC on which you purchased it. You cannot transfer that license to another PC. You can upgrade any components or peripherals on your PC and keep your license intact. You can replace the motherboard with an identical model or an equivalent model from the OEM if it fails. However, if you personally replace or upgrade the motherboard, your OEM Windows license is null and void.
I have it installed on three different computers at home and have not experienced any problems. I also build pc's for customers. I installed the OS in dozens of pc's without any problems. There have not been any problems activating after installation.
Recently I pulled a hard drive from my wife's Toshiba laptop and installed an old Kingston ssd that still had the OS from when it was installed in my personal rig last year. I popped it in the laptop and did not have any problems with activation.
I have not experienced any problems with Microsoft updates either.