Welcome here, Klewer!
The "around-the-campaign-flying" stuff is:
1. you get promoted; I think more quickly when you complete your mission tasks
2. you receive medals like the "Pour Le Merite (Blue Max)"
3. you can fill in claim reports, and they will be decided about by the high command
4. you can add some sign or whatever to a skin, or even make your own one
(this needs additional, freeware programs)
5. you can choose from very many Squadrons / Jastas / Escadrilles
You can set up the sim in the "Workshop" to your likes; actually you can make very
individual settings to make it more or less difficult - much more can be done here than
just to choose between easy, medium and hard.
When you should get into it, you might later set it up very realistic. And then, believe me,
it will be tough to survive 17 hours. So it is a sim for a long time player/flyer.
But you must never go there, if you like it more easy.