Your questions are much too vague to give detailed answers, but here are general ones:

1) this steel is not corrosion resistant.  Like any other untreated carbon steel, it will corrode in air.

2) inorganic coatings, organic coatings, or electroplating could be used.

Could anyone tell me 12L14 steel's stress corrosion cracking rating.  I have looked everywhere with no luck.

Ferritic steels like 12L14 are not really subject to SCC in the same way that austenitic stainless steels like Type 304 or 316 are.  Carbon steels are subject to SCC in hot nitrate, hydroxide, anhydrous ammonia,  and carbonate/bicarbonate solutions.  If this is the environment for the component of interest, then you should consider an SCC threshold.  I doubt that this information exists for 12L14 in the public domain.  You may need to perform a standard test, such as ASTM D 807.

If you are considering plating, I would like to mention that leaded steels, brasses, etc. cannot be plated as readily as non-leaded alloys.  A normal acid activation procedure involves a dip in sulfuric acid, which leaves small areas of lead sulfate on the surface. This results in non-adherent plating, e.g., blisters.

If you cannot switch to a non-leaded alloy, at the very least please warn the plater in order than an alternative procedure (more expensive, but better than defects!) be used.
Thanks,
Ken