Removing this palm (queen sago) (Aus)

Hi all, wanting to know how I should go about removing this palm?

How deep below the surface would I need to get rid of for new grass to take, and grow? Will the stump affect grass growth?

My plan is to remove and extend the lawn to this section (buffalo grass).

After removal, what process do I use to get the ground ready for buffalo? Top soil then buy a few mats of turf?

Any help appreciated.