Unknown Glitch?

[Sekel]

when it wrapped around, how high was the positive number? 1? 0?

Since for mana count is used signed number, it wouldnt wrap around to 0 but to highest positive numbers.

does it work with full pots or does this bring it back to the small negative?

Full potion simply sets your life / mana to your max life / mana, so drinking full mana potions would set your mana back to max mana (no matter whether it is positive or negative)

and how many small pots did it end up taking?

Depends on character class and amount of negative mana.
Clvl 47 Warrior with -111 mana loses 1400 mana per 100 small blues, so its average -14 mana per potion for him.