I'm not sure if AEB-L is the most appropriate material for a cake knife... in other words, it may be a bit of overkill.
It is correct that some stainless steels are in fact MORE susceptible to rusting/tarnishing if not properly heat treated. That said, ANY stainless will typically "stain" or rust regardless, if it's not properly cared for and maintained.
If I were making a cake knife, I'd want it thin and flexible, with a little bit of spring to it. Heck,6Al-4v titanium may even be a good option.
It takes a relatively decent polish, is light weight, corrosion resistant, food safe/hypoallergenic, and naturally durable and springy without having to heat treat.
The "springiness" is desired not so much for function, but more for durability.
BTW, where abouts in Indiana are you located?