Wow Tango.....Im jealous.
Ive been into the traditional hot rod scene for quite some time, and I cant tell you how rare it is to find a bike with "patina" that is so even and perfect as it is on your bike and I am so stoked to hear your going to keep it that way! Rubbing her down with oil is a great idea, or the other way to preserve the patina is go down to your auto parts store and pick up some semi gloss clear coat (just a normal spray paint type), wipe 'er down with paint thinner, and give it a shot of that. This way, it will maintain that perfect patina look, not rust any further, and because it makes the finish smooth and even, it makes the bike easy to clean as well. Just an idea.... Great start and keep us posted!
-Dan
P.S. if you decide you want to bob that fender, try it on a different one first and mount that to see how it looks so you dont ruin the original...not cuz its hard to replace, but because you could never exactly replicate the matching patina of the orig. if you dont like it.