When you buy a new oven, what are the steps that must be taken (other than toveling grates) before using it?
When buying a new oven, and there is no issue that the oven was used to bake non kosher food, then the only issue would be tevilah. The halacha is that we only have to tovel utensils that come in contact with the food. Therefore you would only have to tovel the oven racks or trays if you are going to place food directly on them. This is even if the tray or rack will be lined with baking paper or silver foil. You do not have to tovel the stovetop grates, since it does not come in direct contact with the food, but only with the pot.
Y:D 120-4, Minchas Shlomo 2-66-(5), Chayei Halevi 4-62(12).