Sub-flooring is normally 3/4" plywood.
If the new project is to be tiled with ceramic natural stone or any mortared product, additional sub floor to a minimum of 1-1/2" thickness, should be installed.
If the project is to be tiled, think about whether you want to start in the center and proceed out on all sides to have an equal size tile at each end, or if cabinets are in the plan, you can start with a full tile, because of the cabinets protruding from the wall.
A new trend becoming very popular is hardwood kitchen floors, which, in my opinion is OK but perhaps a tiled section directly in front of the sink and at exterior entrances for obvious reasons are called "wells" and they look classy and practical.