Ways to build habits for an application?

Hey everyone, I am working on a side project right now that is focused on connecting people with short supportive voice memos (https://goodword.club). The app asks you a simple prompt based on time/location and you record a short voice message and send it off into the ether. You will get randomly paired with someone else who also sent out a "Good Word" and from there the conversation can continue or expire. Its just a simple way to support other people across the world in a passive manner. Think like Racket + Tinder (but just the matching part)

That being said you can see that the critical point for this is that people record and sent out these positive voice messages so that they can be paired with someone, but I am trying to think of new ways and verticals to keep that engagement and people sending messages. Here is what i have so far:

Twice daily I have notification reminders to send out a Good Word, questions are directed more towards "What are you goals for the day" and "What is something you are proud of today?" respectively.
I have notifications for when you are matched so a response can hopefully produce right after.

I was brain storming with other ideas of having like a mid-day reminder of like "1,500 people have sent out Good Words today! Send Yours" or having that metric shows on the app itself to encourage that behavior of sending out a Good Word.

I obviously dont want to spam users with push notifications, but I am wondering if anyone has any other tips for driving engagement or behavior in any app!