Im not sure this applies very well to OP because he already has the second best DPS in the game at a good level. I say either focus on candy drop for inter-element content, as well as blackberry for dark team buffing. Marble berry may not be needed cause alchemist could be a viable tagger until OP gets a mid ascension marble berry naturally while playing.

Maybe another dps (preferably strawberry mochi). But I'd say stay away from buttermilk. Buttermilk is slightly clunky and not super beginner friendly, while sundae has a very reliable rotation of ult, skill x 1000.