Oooh… that’s a yummy looking recipe. I might have to give that a whirl.
IMO, to get a noticeable cinnamon taste for that amount of batter, you’ll probably need between 1/2 tsp and 1 tsp. Start with 1/2 tsp, then taste the batter to see if you like the flavour and keep adding a little more cinnamon until you feel it’s cinnamony enough… keeping in mind that the baking will probably tone down the overall flavours. (Yes, I know there are raw eggs in there… but short of eating the full bowl, you’re unlikely to make yourself sick from eating the batter)
No need to add/remove anything to compensate, BTW. Spices are pretty forgiving, since the quantities are usually too small to affect the texture of the final product (it’s rare to add more than a teaspoon or two of any dried, ground spice).