Yes, the strainer comes out and it also separates into 4 pieces which makes it easier to clean.
I would think the garbage disposal would have its own drain cover. Something to check out. I don’t have a garbage disposal. But this strainer is a custom fit into itself.
No, it does not include a flange.
My handy man installed it but I didn’t see any plastic; rubber & metal yes, but I did see any since I didn’t do the install. However, whatever pieces & parts were included, it worked beautifully, as expected & like a Blanco sink & basket I had previously.
The basket strainer will not work for a garbage disposal. The sink waste flange is specifically for the garbage disposal drain and can be used for your disposal unit.
It may work or may not, this product fits most universally-sized drain holes at 3.5".