Take the game at your own pace, play it the way you think it's fun rather than whatever anyone else tells you on how to play. You're not gonna make everyone happy, just make yourself happy (but not at the expanse of blowing up the FOB with an OB during a siege for dem kills.) Also if you wanna play a support role take a look into either Medic or Engi since those two are lifesavers, Medics more so and people tend to not annoy the medic. And for the last point, FF. Everyone no matter how robust has had a situation where they've killed more marines than the xenos have due to a bad nade. So don't worry about FF, kills are kills so you gotta get dem K/D stats up