One suggestion... if you know how... Make the number of hearts displayed depend on the character's level, to simulate how it works in Zelda. Level 1 characters will start with 3 hearts, then gain an additional heart at level 5, and another one every 5 levels. It works out perfectly this way, the 20th heart will appear at level 85.

When the next expansion rolls around, perhaps change it so you get your first heart at level 10 if the new level cap is 90, or level 15 if the new cap is 95.

I haven't actually tried the addon... if it already works this way instead of always showing 20 hearts, please disregard this comment.