Hi,
As read from description, I can do every task that is required in complete and quick way for you.
Here is breakdown of details:
1. Since project is running on heroku, i presume there is enviorement where we can change facebook token
2. Fix captcha on any issue that there is
3. We will set node engine to be run on node 10
4. Stripe api will be updated to latest api. I have done various stripe projects from basic form payment to custom system with percent deduction and money return.
5. I will be giving you advice how to scale, and potentially how to go away from heroku so you can reduce your billing costs, and have similar running instance with a fraction of price.
As you have also mentioned, that firebasedb is being used, its not a problem since i have also experience with it.
If you are interested, contact me on this task.
Thanks.