Congrats on your retirement Don! I've got a couple more years to go...
Good choice on the gift! I really like dBpoweramp. You also have the choice of Uncompressed flac, which sounds like an oxymoron. 'Uncompressed is a special compression mode with stores 16 bit audio in an uncompressed state.'
Once you select your compression level, tick the 'Verify Written Audio' box. It will compare the compressed file to the source.
Here is a great site for all you want to know about flac.
https://xiph.org/flac/index.html"Why do the encoder settings have a big effect on the encoding time but not the decoding time?
It's hard to explain without going into the codec design, but to oversimplify, the encoder is looking for functions that approximate the signal. Higher settings make the encoder search more to find better approximations. The functions are themselves encoded in the FLAC file. Decoding only requires computing the one chosen function, and the complexity of the function is very stable. This is by design, to make decoding easier, and is one of the things that makes FLAC easy to implement in hardware."