As to the welding and passivation of ss alloys: When I say all should be passivated I do refer to marine
use where the appearance is generally considered as important as the part itself.
Many of the newer welding electrodes are self-passivating to a certain extent and show no major oxidation over the years even in highly corrosive environments. This is not to say that the weld is totally protected because the steel
in the original component gets re-melted and re-deposited, thus the edge of the weld often shows oxidation.
Look at the alloy content of most stainless and you will see that the chromium content is quite low, thus the 18-8 designation. Cut the end of a piece of 304 or 316 and watch it rust without passivation. This rust will also be superficial, as this is not the corrosion
that destroys stainless but that discussion is not the purpose of this thread.
As to not storing of mild steel next to stainless I don’t buy it. I won’t buff stainless on buffing wheels that have mild steel on them but I don’t think that contact with a piece of mild steel while out on the rack will cause anything to happen to the stainless other than as I said before: If you scratch it, it will bleed unless you remove the surface iron with an acid.
As to my abilities, welding or otherwise, I don’t blow my own horn but let the facts speak for themselves.
I don't have a lot of time on my hands so good luck to you.