Use facets and autocomplete

Before you add at least one Search API endpoint there will be no possibility to add facets nor autocomplete, because they require search api display plugin for them. Each Search API endpoint derives into search api display, that can have its own facets and autocomplete elements.

Facets

For example if you have 2 search api endpoint, then on facets overview page (/admin/config/search/facets) you will have 2 sources for facets:

Even if search endpoints reference the same indexes, it is possible to have different facets per search endpoint, or the same facets but configured differently. Search results response will follow all the settings that were made to facets.

Autocomplete

Autocomplete settings are part of Index settings, that you can find here /admin/config/search/search-api/index/<your_index_machine_name>/autocomplete. On that page you will find all search configs that reference current index:

Each search endpoint can have its own configuration for autocomplete. Plugins for autocomplete suggestions can also be provided by contrib and custom modules. Here is how the configuration page looks like: