rest is gravy

Translations
остальное - это бонус
After finishing the main project, everything else is gravy.
После завершения основного проекта всё остальное является бонусом.
Definitions
The phrase 'rest is gravy' means that everything beyond a certain point is extra, a bonus, or an unexpected benefit. It suggests that the essential or most important part has already been achieved, and anything additional is just a pleasant surplus.