I bought the Spidey pack. Got 400 splinters and unlocked Storm. Wife and I play coop using those 2 characters.
After closed beta ends all progress is wiped ahead of open beta. I keep Spidey and 2nd costume. If I spend the 500G it is supposed to refund.
Will get a new 400ES to unlock another character such as Storm. Progress in open beta supposed to carry over to live.
People on the beta forum are asking about coop with each person using their own account but unclear if that will get implemented.
Also your friend will need a PSN full account. Not a sub account of yours. My wife's account was initially a sub but I upgraded to a full.