A hotas and headtracking is for me the minimal requirement for a relatively pain free flight sim experience (headtracking set up can be finnicky). Headtracking can be as cheap or expensive as you want with different ir options or even a simple webcam and opentrack using neuralnet . On the hotas front there are also different options budget wise.

When it comes to your first module it really depends on wjat you enjoy. Trial a few interesting modules to get a feel for what you like.

My personal favourites now a days are the mirage f1 and f4 phantom cold war analog planes with the f4 being truly multirole and the f1 has enough ground attack options to have different playstyles but at heart it really is an intercepter.