Have a look at the :merged function in the reference.
It looks to be a bit of a struggle to merge multiple API calls in a single search, so the thing to do would be set up a custom state for each API (make it a list) and then Set the states in the work flow. The repeating group would then merge these all together.
So… Custom States, Repeating Group, :merge would be the way you could go.
If you start building this in the forum app it will be easier to help ! This is fairly complex for a first attempt.