First of all, let me start saying that what you have here shows a ton of potential and that I can completely relate with the frustration : p. My involvement with videogames began with the XNA days, had to do serious graphics programming, gameplay, content loading, etc. Implementing 'shadow mapping' (a thing from the 80's…
So glad that you like it! For the 'median' filter, I would do it would be on the texture itself, inside photoshop. What game engine are you using/panning to use by the way? The 'flares' for example would probably be easier inside there (just additive/screen front facing planes and rectangles, cheap and dirty and…