Hi Sarah! Thanks for the invitiation. :)
A weekly check-in thread sounds fantastic. Maybe have one thread where people discuss their goals, why they're aiming for that, when they want to achieve it by... then have the check-in thread where people can discuss how they're doing?
A thread for inspiration pieces sounds like a good idea, somewhere people can just post items that they'd like to get or think might be nice for others to treat themselves to when they reach a goal.
Challenges sound good, too.
I think just having a team that supports each other whilst working towards their goals would be great! Keep it simple. :)