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Don't sweat it.
When I harden in oil, the oil is just room temperature. For stainless steels, the HT process is much trickier, but for simple carbon steel it is pretty robust. For O1 just heat to...

I don't get the question. You can get a 1" wide razor out of a 1" wide piece of stock, minus a margin that you hone away.
1/4 is thick enough for up to 1".