>>539825668
6/8 (everyone except top right and top bottom) are units from the first year of the game's life. They're useable, but since then a lot of stronger characters that replace them have been released. Also, half of them are wearing skins; that's not what their base frames look like lol.
>Are the vanguards not "real" characters or something?
As far as I know, all vanguards in the game are uniframes. They're an old type of characters back when kuro tried experimenting with that, but they haven't released any new ones in a long time, so it's safe to assume they're scrapped.
Teams are built around elements, so if the the characters have the same element then you can run them on the same team, but ideally you'd want a dps, tank, and a supp/amplifier.

As a new player, you'll be able to farm enough currency to guarantee a copy of every newly released character, so just ignore the older ones imo. All of the units (aside from collab ones) get added to the standard banner after their initial patch, so that, plus the selectors we get every now and then, means that you can grab a lot of them if you really like them.
You get currency from the dailies and weeklies just by clearing stages, so don't worry about the leaderboards in game. All the important rewards are obtainable for f2p players.