Inviting a friend to your game through Steam invites them to your party but not your game. As well as joining a game as the leader of a part doesn't bring the members of your party with you.
100 credits per level up is an abysmal amount once you get to a higher level. As you level up it requires more xp to rank achieve the next rank, thus your credit income slows drastically the more you level up. I was thinking the higher level you are the more credits you make when ranking up. It feels near impossible if I want to save up for any 1000+ credit item after level 15.
If you walk directly into a crashed helicopter you can move it around the map.