[WNC Goater]

I have no problems experimenting and especially with old files rather than expensive steel. That in and of itself isn't foolish necessarily, it's how we learn.
But, IF you are going to try water quenching, I'd suggest a brine solution, heated and don't try edge quenching. I'd also maybe suggest not doing your initial bevel grinding, but save that after the tempering process. My (limited) experience in brine quenching yielded less than satisfactory results. Make no mistake, you WILL get a nice hard blade, but.... The times I've tried it, post grinding, resulted in some pretty significant warping and worse, a "wave-warp" which was impossible to remove and resulted in a broken blade. Just plan on dealing with warping at the very least.
Grinding out the profile and quenching before the bevel grinding would be less likely for any significant warping(though I never tried it before beveling) and IF you get a break, you haven't lost all that time and effort of grinding your bevel.

I've never heard of anyone trying specifically edge quenching in brine however, but suggest reading Doug's response above again.