Hi Day, Yes, you can. Just adjust the baking time since cupcakes bake faster than a whole cake. Start checking for doneness at around 15-20 minutes, depending on your oven and the size of the cupcakes. Keep everything else the same, like the oven temperature and the batter composition. Enjoy your baking!

Yes . Canola oil works just as well.

What kind of oil should I use. Is canola oil ok?

Hi Carmen.
I believe this has to do with the acidity of the buttermilk and the cocoa powder. By folding in the baking powder and baking soda at the end, you are ensuring that their leavening power is fully utilized when the batter is baked. If you add them earlier on in the mixing process, they may react too soon and lose some of their ability to help the cake rise, resulting in a dense cake.
I hope this helps! Do let me know how it turns out for you!