Cove lights look simple, but the decisions have to be made before the gypsum goes up.
Cove lights and false ceilings are common in Bangladeshi flats, and they can look wonderful or harsh. Most of the difference is decided before the ceiling is closed.
Think in layers. A cove gives a soft general glow, downlights give focused light where you read or cook, and small accents pick out the things you love. Each layer should have its own switch so a room can change between evening and daytime.
Decide where the furniture goes first. A downlight belongs over a table or a reading chair, and that is only possible if the layout is settled.
Keep drivers reachable and make sure the ceiling board suits damp areas. Think about load-shedding too, and decide which lights should stay on if you have backup power.