You can set and name your unit on this screen.
Base Performance stats is not affected by card color and equal for every color. Bonus performance [indicated by (+****)] is affected by each card Lead skill.
SSR will give large boost, SR will give medium boost and R will give small boost. Evoluted card will not increase the boost bonus (ex: SR evoluted to SSR will still give medium stats boost)
The recommendation to maximize the performance is setting a unit with same color card and high rarity.
If that's not possible, mixing card with high rarity and level will give better performance than same color N team.
You can also press the pink button to let the game select recommended card and costumes for your team.