Personal choice. Me - I don't like the sapwood contrast. Outer edges mutch more aesthetically pleasing to me than sapwood down the center - looks like a racing stripe on a SuperBee. Your call.
On ripping for center match:
1. pick a common grain ref point both ends, both pieces - somewhere you know the grain matches.
2. Measuring from those ref points, rip inside waste, but leave 1/4" + extra waste.
3. Now you can butt them together, and start running the blade down the common seam, as suggested way earlier. Will take 2+ passes.
4. Keep it up until you have a perfect match.
5. Slip/slide the 2 pieces to get the book matching correct.
6. Glue it up.
7. Trim the ends.
When I started woodworking, I didn't know squat. I have progressed in 30 years - now I do know squat.