How much rebuilding do you want to do? Among other things, those factory guns are known for having way way way too much wood on them, incorrectly profiled, as well as having parts that might need changing out.
A lot of times, it's actually easier to start out with an entire scratch build from a blank than it is to try and fix someone else's mistakes.
Then, if you want to try your hand at carving and engraving, well, that can really really get in to chewing up the time, but at the same time, expand your skill set and let your creative side come out.
Do a search here on browning and finishes and check out those threads. There are a zillion of them here. Browning isn't the only finish available for the metal however. There's natural white, or shiny, hot bluing, graying, blackening, rust bluing, hot and cold browning, and case coloring (though that's mostly for parts rather than barrels).
When it comes to stains, the "go to" finish for most is Aqua Fortis, especially for maple. Not sure how it works on other alternative woods (beech, birch, mystery hard wood) except walnut, where it will turn it black as coal. Nothing brings out curl in maple the way this stuff does.
When you're getting in to stains other than AF, the sky is the limit. Stains, dyes, gel stains, soot, paint flecks. It's all over the place.
For top coats you can go with oil finishes, or varnishes. Some people mull paint pigments in to their varnishes to create a "red violin varnish" finish. You can spend a week or more researching this stuff.