1. There is no rule as to which part of pork to use. As long as it is not for stewing, you can use any kind. I sometimes use thinly sliced pork belly.
You could use beef or chicken instead of pork, or mixture if you want. But the meat needs to be thinly sliced.
You could also use seafood such as squid, prawns, scallops. In the case of squid, I find that slicing it into thin strips work the best. You may also want to slice prawns and scallops thinly if they are large.
2. Bulldog brand tonkatsu sauce is available at Asian/Japanese grocery stores. It is like a thick sweet Worcestershire sauce. You could also buy sauce specialized for okonomiyaki at Japanese grocery stores if you wish. Okonomiyaki sauce is sweeter and less spicy than Tonkatsu Sauce. As a last resort, you can substitute with a mixture of Worcestershire sauce, tomato sauce/ketchup and sugar (2:2:1 ratio respectively).
3. This is Japanese mayonnaise which is quite different from Western style mayonnaise. It has less acidity in it and the flavor is enhanced with umami. You can buy Kewpie mayonnaise at Asian/Japanese grocery stores and sometimes at super market in Australia.
4. Aonori is dried seaweed flakes and benishoga is red pickled ginger. In the section “About Yakisoba Garnish” in my post Yakisoba (Japanese Stir Fried Noodles), you can find more details of these ingredients.
Although these are optional, I strongly recommend to eat okonomiyaki with them on top as it enhances the flavor of okonomiyaki.
5. The reason for taking a little bit less than half of the total quantity of batter is that you will need a small amount of batter to pour over the topping. You don’t need to be accurate about the quantity. If you took too much for the first pancake, then make the second panbcake slightly smaller. But make sure that you leave a small amount of batter when the batter for second pancake is placed on the pan.
The recipe is to make one pancake at a time but if you are making two at once by using two frying pans, a BBQ iron plate or an electric teppanyaki plate, then it’s easier to equally divide the batter. But don’t forget to leave some to spread over toppings.
6. If you have a hot plate like mine or a portable cooktop which can be placed on the dining table, then you can leave the pancake on the plate or the fry pan, add sauces and garsnishes and turn the heat off. You can then divide the pancake to eat directly off the plate/fry pan which is more fun!