Hm, I don't think I agree completely with the two answers above.
If you get a bunch of people that do as you say, and you have them fight for you, they are a gang, with stats depending on their fictional facts. A medic's two orderlies, not used to combat, would maybe be a-guy-or-two 1-harm 0-armor green or something. But if you "have" a gang in the fiction, you have a gang, simple as that.
Getting pack alpha, on the other hand, says something about your character's leadership style, rather than what her underlings are like. When the character's gang says, "no way we'll do that, boss, that's suicide", the character with pack alpha will just smack them until they know their place, while a character without has to reason with them, use some sort of leverage to get them to do what she wants, probably rolling manipulate, but possibly going aggro.
So, getting pack alpha is the character getting a new schtick, and I'm pretty sure I'd make her spend an improvement to get a move from another playbook to get it.
But getting a gang, go ahead, persuade 60 people to follow you into danger and you have a large gang, no sweat.
The thing with having gangs on your sheet that are either a central part of your playbook or that you get from an improvement is that it's a bit of cheating on the MC's part to take them from you too forcefully or too directly, because that often means taking away what makes the character cool, and that's no fun.
Those 60 bastards you just manipulated into following you into an ill-advised raid? No such considerations, so watch your back! :D