Welcome and glad theres someone so hyped about the game. Regarding the "invalid code" thing, i am not sure. Could be just because the feature of the free syandanna is quite old so the links could have gotten lost in the world of links.
There is voice chat you can use in public games, but its very hardly used from my experience, so unless you set up a squad of sorts, or get lucky and they start talking once you do, i do not think youll find talkative squads.
I am not sure which button it is to activate voice chat, especially not on PSN, so would have to look into the settings yourself.
When you have questions about the game, youre of course free to check out some yt videos, ask here, or maybe even better, in the Q&A chat in-game.
A little P.S: I think the free rewards are mostly cosmetics so its alright, but id recommend to not use platinum you get for cosmetics, at least not yet~
Other than that, welcome to this hectic world and i hope you continue to enjoy it from now forward.