Max Bucket = 16 with min shading rate = 0.2 will make your tiles 1280 pixels. Changing your shading rate to 1 will reduce your tile size to 256 pixels with negligible impact on image quality (unless you need something finely traced; then you can set min shading rate on a per object basis).

Turn off raytracing. Fake your reflections using reflection maps.  Render one object at a time. Create a separte shadow pass and composite in Photoshop.

Edit: just noticed that you aren't raytracing.