I have included maximum possible fields while creating the search index to be safe in case I need to retrieve those fields in future. Many fields are not currently searchable and retrievable. Does having more fields not retrievable, searchable, filterable, sortable and facetable in Index reduces the search performance?
Yes, both indexing and search will be affected by having more fields. Obviously, the less features those fields support the less work the indexer has to do. If the field is only retrievable you only have to store that data. If it's searchable you have to build the index.
As an example, I tested the same data with 2 fields and 1000 fields. Indexing performance went from around 1300 documents per second to 30 documents per second. I'm expecting the total amount of data to have the biggest effect on indexing performance.
The query performance is negligible.