I'm looking to make a cutting board using 2 types of wood in cubes. I'm looking to use 2 contrasting types of wood. I will have the end grain as the surface. Should I use soft or hardwood? I plan on buying from Rockler, I'm looking to use White Birch, White Ash, White Oak or Hard Maple with Black Walnut, Cherry or African Mahogany. Also I'll finish with vegetable oil, will these woods still be food safe? Thanks, Phil