Well there is always many opinions about such things so here is what works for me.
As for rust a couple of swabs with Evapo-Rust will take out flash rust, if its crusted up good an over night soak will make it disappear. Always remember to clean out the Evapo-Rust real well, I am not sure why but do it as the old gun smith that taught me was always right so I do not want to find out the hard way.
When it comes to keeping rust away I have tried many things, I learned the hard way about Rem oil in muzzle loaders, but still use it in the mechanism and my cartridge guns, on my muzzle loaders I have tried Ballistol and it works OK but I prefer Barricade for normal times between trips to the range and hunting and I use Birchwood Casey Synthetic oil for long term storage.
The reason I prefer these is a combination of reasonable price and the fact that a quick wipe with alcohol will get them off the barrel.