I was trying to do the same thing with units. link their mana directly to heroes mana... but I found out you can only set the mana to a figure under the units max mana.
so first set Your heroes max mana to 1000 and then set current mana to 1000 set mana regen to 0. then set a generic unit event for acquires mana potion, uses ability. whenever this trigger is triggered, it will set mana max mana current to 1000 and mana regen to 0
I hope this helps cheers.... vm me for further help