Thieves' Night

Not a puzzle, but in case you can't open the door with a red knob, the key is inside a drawer on the living room.

In the single bedroom, there's a note saying the answer is on the paintings. On the second floor, there's many paintings across the corridor, interact with then and follow the year order from the oldest to latest, and some of them will have small drawings somewhere. The correct order of the buttons is:

Bottom Middle/Moon
Top Right/Triangle
Bottom Left/Star
Middle/Devil?Cat?

In the master bedroom, there's a note saying you can find the combination to the padlock on someone's latest work. After you enter the atelier with the Flower Key(found inside the wood box), there's three flower paitings on the wall. The note says the answer is red, yellow, blue. The center painting has red, yellow and blue flowers, so you need to count how many flowers of each colors it has.

The answer is: 536