No worries!
Yes, we recommend deleting any v11 tags or any v11 cards that are not imported from v12 as they are duplicates or extremely low yield
To remove v11 tags: How to remove V11 tags when upgrading from V12
To remove v11 cards: How to Delete old v11 Cards
Yes this is correct. We recommend the UWorld QID add-on to quickly search UWorld QIDs and get the corresponding cards. Its included in an AnKing VIP subscription (separate from AnkiHub)
I used the UWorld QID add-on and found cards for QID 13600
Put this in the anki browser and see if something comes up: tag:*UWorld*::13600