resolve index strategy for data

I need help to make all possible combination of search queries to be fast when querying my data. I have normalized my data structure as much as possible, on my opinion, so it needs the least amount of indexes possible. I also have some ideas of indexing strategies we could try to achieve the requirement. I'm open and willing to change the data structure, or the way the query is done, or anything else as needed to achieve the best possible strategy for indexing data and make all searches very fast. My current DB is MongoDB, so preferably to find the best strategy for it (although I'm open to change DB if really worth it). The estimated amount of records we will have on production environment is about 8 millions. I provide attached an example of the JSON data with 1 record as "[login to view URL]", just to give you an idea of the current data structure. My indexing strategy idea and explanation around it is in the attached file "[login to view URL]".