First version: what must be in
Whole across one, not half across three
One flow that works end to end — entry, action, result, message — beats three flows each stopping midway. A user forgives what's missing; they don't forgive what looks present and doesn't work.
What always goes in, even minimally
Failure states. What you see with no network, when a save failed, when there's no data yet. A blank screen with no explanation is a bug.
The ability to see what happened. Basic logging and error reporting. Without them, the first complaint is a blind investigation.
Backup and restore. Before there's real data, not after.
Security basics. Encryption in transit, passwords stored properly, permissions in the server and not only in the interface.
What can wait
Polished design, user preferences, export formats, multiple languages, an admin panel. Most of them can be done by hand in the first weeks to see whether they're even needed.
Going deeper
Define in advance what will make you expand and what will make you stop: number of active users, completion rate, support volume. Without a written threshold, any result will be read as justification to keep going exactly as you are.