There is a lot to unpack here, but I’ll try my best.
First off, I am not aware of any C# examples unfortunately. Hopefully someone else from the community can chime in with a good example, or if not, please do feel free to help contribute to the community!
If you are trying to search a hashtag or for specific posts and users attached to those posts, you can do so in either realtime or historically.
Historically - You are going to want to use the Search Tweets APIs. We have a lot of information in our documentation that should help you out.
Realtime - You are going to want to use our Filter Realtime Tweets APIs.
If you are trying to lookup a user’s information, you are going to want to use our either GET users/show or GET users/lookup.
While we do include some engagement data in our Tweet payloads, you can pull in-depth engagement metrics using our enterprise Engagement API.
Please let me know if you need anything else!