I usually make stuff from scratch and follow vegan recipes so i don't have to "veganfy" a recipe. Like my family loves Nora Cooks in general and there is a great nora cooks pancake recipe . We've made that as pancakes but usually go the waffle route. It's pretty easy to make and leftovers are great in airfryer (ok in microwave). We usually make extra and have leftovers for 2-3 days
If i need to do a conversion on the fly i usually just do a quick internet search, check 1-3 sources and go with the consensus. My search is usually "[x] to [y] substitute ratio" or similar.
For your plant milk i would generally go 1:1 but it would depend on the type of plant milk since some is thinner than others. If you can't find anything specific then do your best guess and treat it like an experiment, take notes, and adjust next time. For your specific case this post seemed fairly detailed, mentions usually 1:1 but goes more in depth. For the things i usually make though 1:1 seems to work fine for our Almond or soy milk.