As far as whether or not brine should be heated, my experience with it, which was some time ago, was to heat it to about 160? before quenching. I can't say that it is a must but the few blades I quenched in brine didn't break.
As far as how many times you can put a blade through the austenizing and quenching process before before you make some irreversible change to the steel I would say that there really isn't one but with a caution that you might accidentally refine the grain of a shallow hardening to the point where you're not going to get any hardening. And that's a big might. If that happened all you would have to do is heat the blade up to where there is grain growth and then try to bring it back down a bit.
Doug
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