How to make my datasource multi-instance

Good luck! The main thing to remember about Active Discovery is that it needs to return a list of instances, with a minimum of two values per instance: some kind of unique identifier and the displayName. Whatever unique identifier you choose will be addressable in the rest of the DataSource using the token ##WILDVALUE##.  ##WILDVALUE## is used to tie collected data back to the instances, so whatever you use for discovery should match what you use in polling. Whatever you choose as the displayName will be addressable in the rest of the DataSource using the token ##WILDALIAS##.