It wasn't Walnut, but for my alder body, I used Tru Oil. I just rubbed it down to an even matte all across the body, then used Birchwood Casey Wax over the entire thing. Sort of a nice sheen. Not a mirror finish. Don't look like it's gooped in gloss.
Also, if you want protection from hard things, Tru Oil was the WRONG choice. Any type of oil was the WRONG choice. I like small dings, belt scratches. It's up to you.
As for lemon oil, I've never heard of it used as a hardener. If you really wanted to get deep into it, ernieball forums are a good place to go. If I remember correctly, a majority of the musicman guitars are made with tru-oil necks, and some of those guys seem to understand the stuff alot.