Your ask for advice is overly broad but if you can provide more details on your use case we may have some suggestions. Some of these questions will be better as separate discussion topics with specific examples.
If you need more advanced text-based search with features like fuzzy matching and autocomplete, Atlas Search is nicely integrated with MongoDB Atlas. An example of your desired search features would be helpful context for any suggestions.
Setting up the ‘right’ mongodb
Do you mean choosing a deployment topology (use at least a replica set for production), version (start with the latest GA release), or something else?
Weighing up Atlas Search vs using something else like Spinx
If you are already using Atlas, Atlas Search is the obvious choice. Using Sphinx or another search solution will require finding (or creating) a connector to MongoDB. You can sync data using change streams, but I expect building a sync solution isn’t core to scaling your application.
Setting up performant indexes including the use of wildcards
If you need help optimising a query, I would start a new forum discussion topic with relevant details (server version, query, sample indexes, full explain output). Atlas Search has features for partial and fuzzy matching and uses different indexing strategies to improve performance (the underlying implementation is Apache Lucene).
Reporting → should I be looking into Data Lakes
That really depends on your use case, but if you are just getting started I would focus on your core understanding of MongoDB before adding too many other services or optimisations.
You can ask questions in community forums, but there are no guarantees of timely responses or that someone with the relevant expertise will see (and have time to answer) a more niche question. If you can start with shorter and more specific questions, I expect you are more likely to get faster responses. For example, this post is asking a half dozen questions which are a larger than average time commitment if someone wants to respond to all of them.
I would also focus on creating clear titles for your discussion topics as that is the main context another community member sees before looking into a discussion. For example, this topic might have been more appealing as “Advice on scaling from 6.5 million to 500 million documents”.
If you want predictable support with SLAs for a business use case, I would look into Atlas Support Plans or Flex Consulting.
Since you are relatively new to MongoDB but want to scale a production use case quickly, I highly recommend getting professional advice or training. You can certainly take the time to learn everything yourself, but a consultant can provide more holistic advice about your use case and future needs than is practical in community forums. Discussions in community forums are better suited to specific questions that do not require context of your roadmap or overall plans.
MongoDB University courses are free. Are you referring to taking M121: The MongoDB Aggregation Framework or a course from another provider?
There are some course recommendations on the DBA Learning Path and Developer Learning Path, but it sounds like your questions are broader.
I suggest having a look through the white papers and presentations available in MongoDB Resources. White papers are likely more relevant, but if you provide more details on your situational context that would help narrow down the suggestions.
Taking a few guesses at white papers that may be of interest:
Hope that helps!