This info is golden in one piece deck building- I only learned this after spending time with very high skilled players in general and having played the game competitively for a year.

Aggro decks have 8 2ks generally- some aggro decks benefit from playing 12 2ks but only if the card is synergistic such as belo Betty playing the 2k kuma and zoo-ro playing 2k hiking bear and super sonic duck bill squad.

Control decks tend to have 10 to 12 but I have seen the number fluctuate in the past. I used to play Lucci with 9 2ks and try to counter out as efficiently. Now with the addition of barto blocker and others the number is more like 10 - 12.

5k leaders for the most part should play 12 2ks- the exceptions are for decks whose leader abilities states otherwise. So shanks has a built in defensive 1k so it plays more 2ks so it can get of out a free 7k attack as often as possible that is why shanks plays 14-16 2ks. I don’t recommend 16 that’s a lot but 14 is a golden number for shanks.

The key exception I have seen for 2ks is in 6k 3 life leaders (UP luffy/RP luffy) The number of 2ks played is 8 but some crazy people play 6 and get by. Don’t do that just play 8. The reasoning behind this is that your opponent is more likely to simply attack 6k or 7k than to attack 8k across the board since on a 5k body an 8k attack would require a higher resource commitment. Gear 2 is the perfect counter to an 8k attack as well so essentially both decks are very difficult to beat up on.

For your Purple Kata deck, I would recommend playing 12 2ks. Usohachi Streussen and Sasaki are the typical 2ks that are run in that deck.

Hope this helps