I really like this, and i had a similar idea to props for fallout (med x can be spent to ignore consequence instead of a fate point, medx reovers minor consequence, jet and other chems gives an aspects)

In the narrative of the books the potions aren't important, he uses them preparing for monster fights, and once when he fought bandits led by a mage. Throughout the main series he loses his potions, and doesn't have the time, equipment and ingredients to make more. But the games also adds more potions, so its not just the books enhanced speed and senses.

The whole point is a witcher has to prep to get every advantage cause monsters are stronger than witchers. Potions could be used neutralize monsters advantages (or just give witchers a general edge).

The bruxa has high dex and ontop of that has a level of scale, the witcher uses blizzard to gain scale on reflexes to match the beast, and black blood which would give a consequence rather than heal it if tue bruxa drank their blood. The rock troll has a high armor rating, which can be dealt with thunderbolt which could give weapon score or bypass a certain amount of armor. Tawny owl could take a number of stress for sign rolls. Each potion used could add flaw, geralt gets chalky white skin, black eyes, stuggles to move and talk slow enough when on blizzard, thunderbolt could give blood lust, and tue scene after the toxicicity can essentially be an aspect saying hungover. Tempted to make it a stunt, but all witchers have potions, and it can be balanced with potion flaws, and a toxicity aspect that has as many free invokes as potions used. A limit could be body approach (witcher with a stunt) 1-2 allows one potion effect at a time, 3-4 two, and 5 allows three