As far as how many coats, it all depends on the condition of the rest of the gun, good condition maybe four rustings and two boils. I think the most I have done is 6 rusting and 4 boilings. If too much of a sheen, you can use 0000 steel wool. I usually coat the barrels by warming them with a propane torch and then using motor oil on a rag to coat them. It does gives the barrels a slight sheen but at least they are protected somewhat.
I use Laurel Mountain Forge for rusting and I am satisfied with it. My last set of barrels that I did was about 3 years ago.