Hello!
-A little bit of chamfer around all the hard edged objects would help. Cabinet fronts, marble under shower glass, shower glass, maybe tiles.
-Try to find visual references, photos for similar kind of objects. For example, there's no gap between cabinet fronts, drawers, shower door.
-Have a look at Corona Material Library, for metals, ceramics and stones. At least see how they were made.
-Lighting looks a bit flat, yes. First, decide which will be your main light source, then setup a LightMix and play around with all of your light levels to emphasize certain areas and have a bit of contrast/depth.
-I don't know if you have it but try to avoid hidden light sources or unrealistic light shapes also avoid too high white values.
-Add some more color depth to your lighting situation. For example, outside brings blue light, but interior has warmer lights. Having all your light sources pure white takes a bit away from the realism.
-Focus on 1 thing at a time. First get the shapes right, then create your base lighting, then use accent lights, then tweak your materials.
-To have a bit more realistic backplates, again, see some references similar to your lighting condition.
-If you have good textures, correct materials, good light balance, you don't even need to open Photoshop or anything. Frame buffer post production is good enough.
That's it on my side. Good luck.