12 types honestly covers everything I was going for with this, plus what would the matchups be if I added more?
Well, first of all, I don't actually get all the reasoning behind your chart, to be honest, but I'll see if I can make sense of it enough to try to explain how my six suggestions would work (The one I feel is needed the most is Mint, though).
First, I've noticed that it seems that flavors that clash and/or have one overwhelm the other are the ones that result in weaknesses and resistances (in most cases, at least), so I'm going to stick with that mostly in my deductions.
Mint:
Resists: Vanilla, Apple, Banana, Blueberry, Grape, itself.
Weak to: Chocolate, Nut, Licorice, Butterscotch, Caramel.
Super-effective on: Vanilla, Apple, Chocolate
Not very effective on: Orange, itself, Licorice, Butterscotch, Caramel
Nut:
Resists: Banana, Chocolate, Caramel
Weak to: Vanilla, Butterscotch
Super-effective on: Vanilla, Mint, Caramel
Not-very effective on: Banana, Chocolate, Marshmallow, Butterscotch
Marshmallow:
Resists: Nut, Licorice
Weak to: Vanilla, Chocolate, Butterscotch, Caramel
Super-effective on: Chocolate, Licorice
Not-very effective on: Vanilla, Butterscotch, Caramel
Licorice:
Resists: Vanilla, Cherry, Strawberry, Apple, Mint, itself
Weak to: Orange, Lemon, Lime, Marshmallow
Super-effective on: Banana, Grape, Raspberry, Mint, Butterscotch
Not-very effective on: Orange, Lemon, Lime, Marshmallow
Butterscotch:
Resists: Mint, Nut, Marshmallow,
Weak to: Licorice, itself, Caramel
Super-effective on: Mint, Nut, itself
Not-very effective on: Chocolate, Licorice, Caramel
Caramel:
Resists: Mint, Marshmallow, Butterscotch, itself.
Weak to: Apple, Chocolate, Nut
Super-effective on: Chocolate, Mint, Marshmallow, Butterscotch
Not-very effective on: Apple, Nut, itself
Those are rough guesses, but I hope that that'll help if you consider any of them. Also, I'm really happy you like my idea for improving Strawizard. However, another request of mine is another Apple-type PokéSweet that's a dual type (and not part chocolate, this time), as well as making it possible for every PokéSweet to have a STAB move for each of their types (and
good STAB moves, at that). Especially since I noticed that Candino is part Strawberry but can't learn any Strawberry moves. A good reason to add more types is so that you can make Hidden Power accessible (since its formula is based around utilizing sixteen types (ignoring Normal in the regular games, as well as ignoring Fairy in gen 6)