for walnut (and other darker woods), I like amber or garnet shellac -2 coats, sand after the first coat to knock down the raised grain. It brings out the rich color of walnut. (BLO or other oil finishes do a nice job as well). Topcoat as desired -shellac, wipe-on poly, polycrylic, etc.... As always, test your finish schedule on some scrap before adding to your actual work.
FWIW. Movement may wreak havoc on your project. To give you an idea of how much wood can shrink. I built a coffee table out of walnut and maple that was ~24" wide with breadboard ends. After it was finished, and brought into the climate controlled house from my garage shop, the top shrunk across its width ~1/8". The bb ends of course were no longer flush w/ the sides. That's ok b/c that design prevents the top from bowing yet allowing for expansion/contraction.
Sam
