Best architecture - To populate dropdown values

I need to develop Application into Appian platform.

Our UI is having many dropdowns around 20 for search criteria.

1. What is best way to get data from database? using REST service or direct connection.

2. Does all different dropdowns should call different stored procedure or any other way?

3. Does Appian provides Caching so we can define caching policy. otherwise everytime i refresh page then it will hit database to get data.

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