Hi Paul,
Welcome to the forum.
I can only offer some of what I have learned. I don't know Macs very well, but I have copied a lot of vinyl to digital.
What format do you need to play? MP3? what type of program are you using to record?
A major factor in how you create your copies will be how you intend to play them. Because I have a variety of media players, I create multiple formats from my master recording, so I record to a lossless format (FLAC). Since you are on a Mac, you may want to consider ALAC.
I record my master at either 96kHz or 192kHz, but only so that I have the extra headroom for post-processing (removing the clicks and pops, mainly). If you are not going to do post-processing, then you could record straight to 48kHz and save the time and space. You won't hear the difference, especially if your final format is MP3. One of my final formats is 320kbit MP3 from a 44.1kHz down-sample, to satisfy my older media-players, but I keep the original high-resolution versions in 24-bit FLAC (in case I come up with a new post-processing algorithm in the future). A couple of my media players, and of course my computers, can play the masters directly, but it doesn't really sound any better than my MP3 versions.
If you are concerned about space (I'm not), don't need a variety of formats like I do and don't intend to do any post-processing, then you can get away with copying straight to you final format. In that case, stick with 48kHz
As I said, I don't know Macs very well, but my understanding is that the Mac's DAC is good, so it shouldn't matter much whether you use optical or analog. However, my philosophy is to keep the music digital for as far through the signal-chain as you can. But it also depends on what you are feeding it into.