I can help with your opening scene right now :)
Well, first you don't have any setting description or a description of the characters in your opening scene
"ALEX (40s) sits with a bunch of people, listening to a
lecture by DAVE (60s), a preacher."
I might say "Inside a small grey room twelve people are seated in a circle. Out of a window dark clouds blanket the sky. ALEX,40s, stocky but withered fidgets. DAVE,60s, silver, solid, and smiling rises."
(I don't care for Dave's first line, personally. It feels a little empty and doesn't feel sincere either.)
so, who wishes to make the first
step in our little twelve-step
group?
Is this the first meeting of this AA group? Is this the 12th AA meeting for this group? It looks like you want it to be the first, but Daves line doesn't feel like a first meting greeting.
What about, "I'm happy to see you're all back this week for our session. Is there anyone who would like to go first?" (Its not perfect, but it feels more personable.)
No reaction. All the members stare silently. Alex raises his
hand. The Dave invites him with his hand, and he gets up and
stands at the center of the room.
Has a redundancy, All the members staring silently is the same as having no reaction. I t kind of feels like no one wants to be here, but I think if you show these characters fidgeting, or playing with their phones, dozing off, or even staring out of a window that you'll have more life in the scene.
I've never been to AA so I don't know if people stand in a center of the room to share their experience but I suspect having Alex rise from his seat would be enough.
my name is Alex. I'm 44 years old,
and I'm a drug addict, and this is
my story.
I think you can flesh this out a bit more, it feels like the start of a confession, but It needs a little bit of a hook I think. You might consider:
"I'm Alex, 44 years old. Been on crack for half of that...I'm not sure where to start."
This is a fair amount of information and helps convey more character. He's middle aged, he's been an addict half his life, and he has regrets.
But I think these changes help flesh things out a little bit. You might consider ending the scene with Dave saying something and not Alex. Give him something reassuring to say to encourage Alex to continue.