I would like to know the best practices for installation and configuration. We are thinking of 50 servers, what would be the optimal installation and configuration and the limitations that mongo would have
Impossible to say without some idea of how many will be active at what time, what the working set for a given user will be and what will the write load vs read load be?
If you want to benchmark the performances of different MongoDB configurations, you can use MongoDB Atlas to setup different clusters with different number of shards, size of instances (RAM, CPU), etc and run your benchmark to make sure you are hitting your numbers.
But you can only do this once you have figured your data model, indexes, shard keys and most frequent queries which I highly recommend to plan before starting to plan anything else as this will drive the rest.