Pursuing long term ex's close friend.

So It's begun. I'm going after my ex's close friend. (We're both 22)

There's a TLDR at the end, but here's the long part.

It's been about a year since we split and months since NC. She's got a boyfriend and I've been dating around. All is well. But now, I figured I would regret it if I never went for her friend.

Little background. I could tell her friend was into me the entire relationship. I doubt she would've acted on it though (she's a good girl). But also, my ex would mention that her fiend would talk about me. My ex even felt uncomfortable if she was around me.

Now, come some time later, I decided to text her.

I texted with a joking opener, she replied with a joke pretty quick, but in general she takes a long time to reply. Hours and hours. But the texts aren't lazy or anything. They're fine in length and welcoming in nature.

There were 5-10 exchanges and then I asked to hang out. She said "Yeah, definitely". So I asked "Are you free tonight?" She got out late from work and wasn't able. (Also, I know to call, but the last time I said a word to her was maybe last year, so I figured a message was most appropriate).

I asked her when she will be free. I'll just call and ask to hang out whenever she says she's free, since I know I wont be calling during work or something.

Haven't heard from her since last night.

Am I handling it fine? Anything I should do differently?

Also, if it makes any difference, it's on snapchat and she replies when she opens it. And maybe it's weird but I like knowing where I stand so I checked her score and it goes up (meaning she's opening and sending stuff) between the long periods of no message.

TLDR: Going after long term ex's friend. Ex already has a boyfriend and ties are severed with her. Her friend takes a really long time to reply, but sends quality texts.