Hey @OneFromTheShadows! Late reply here so maybe you already sharpened it, but if I were you I would get 50-70% of the grind done, then heat treat. Grinding hardened steel wears your belts out a lot faster, and can destroy your files too if you are filing it down.
Tool steel typically comes with letters before what type of steel it is, that helps identify the hardening process - W for water, O for oil, A for air. As for S, I’ve always known that to be an air hardening steel. I think you can use Oil pretty interchangeably for many tool steels.
So if I were in your position, I would grind down 50% of all sides, then heat treat it. You’d want to normalize it first, meaning bring it up to temp and then take it out of the forge and let it cool slowly (bucket of ash, or something). See if you can file check it to make sure it’s somewhat soft, then grind your 50%. After you grind 50% off, get it back to heat treat temp and then take it out and set it on a fire brick or something to cool off/harden. File check it to make sure it’s hard, then temper it to whatever hardness you’re looking for. Tempering means to heat the steel to lower temperature to relax the steel some, I would bring it to probably a blue in the middle and a straw yellow on the edges.
After that, you can finish the grind. I would be very careful finishing the grind on that thing, it looks like it’d be ready to fly off the wheel and bite your hand! Good luck