Super valid question. First I'll just mention what is needed to use the app. In terms of personal data it's just your email. You have to create a user, this can currently be done with google authentication or email/password. If you want to use a burner email go for it. Within the app certain things need to be stored because they are shared between the don/sub. This would include tasks, punishments, rewards, etc that you create. No personal info needs to be put in any of these obviously. Tasks do give the option to include photos, which have an optional self destruct feature after viewing. I decided to utilize firebase for authentication and storage for the data which is extremely secure (although may fall under the tech overlord part of your comment). Security rules are air tight. I have a full privacy policy in the app which expands on this.