Newer kernels are generally recommended, although in some cases an older kernel might be used for compatibility reasons. If the system works with current kernels there’s no real reason to use an older one.
The instructions for Arch suggest that bcwc-pcie-git is all that is needed (it automatically uses the firmware package previously linked). Installation of the linux headers is presumably likewise automated.
Or, you could install everything as per the manual instructions.
The correct linux-headers versions for the installed kernel should normally be installed. If installing manually, you would also need to install the version-specific linux headers manually.
Aside:- If you would like a deeper understanding of linux headers, then [root tip] [How To] Kernel - Headers - DKMS might be of possible interest.
Cheers.