There's not much I can think of to add to what maotd has noted, aside from suggesting that you pick up Kugaisou from the FG shop at some point. She's a solid source of skill proc (1.28x to 1.36x based on her skill level) along with crit bonuses (+30% crit rate, +35% crit damage). As for Rarity Growth 5* Knights, either version of Larkspur is good if you're looking for attribute coverage.

Original Larkspur is blunt/hit attribute and gains slash, pierce and magic attribute coverage for three allies including herself after RG. Two of her abilities are duds though (+150 speed for the squad and +attack equal to 150% of the squad's speed rating) so it comes down to how much you want the extra attribute coverage for at least three members of that squad.

Larkspur (Halloween) gains pierce and magic coverage but no slash coverage after RG. All of her other abilities are useful though (+25% attack, +20% crit rate and +25% crit damage for the squad, an additional +10% to 30% attack based on the number of different ally attack attributes present).