Serious Eats - seriouseats.com

Every week I roast 4 pounds of carrots at 400 degrees for 90 minutes. They sit in the refrigerator and make a delicious and filling snack with a generous sprinkling of salt.

Dark -70%!

I adjust. If it calls for 2 tsp vanilla I make total volume unless I personally know the mixture is forgiving. Such as tiramisu, flan, custard, ice cream where you are not baking as much as you are cooking.
Also when you are baking cakes you need not relegate yourself to putting the liquor in the batter. Make some simple syrup and add your liquor there. Nothing makes a cake last longer and taste as moist as a brush of simple syrup.
I sometimes even substitute limoncello for lemon zest.
Here is my recommendation for the liquor beginner. First try it in brownies.
Brownies are very forgiving. Try some godiva, kalhua, chambord, grand marnier, amaretto whatever flavor you might like and then try it out. The moister the cake, the easier it is to do. After brownies move on to cheesecakes, layer cake. I am making trifle for christmas and you can use some liquor in that either in the cake or the custard-both (oooh)
Don't be afraid to experiment. Worse that can happen is you get a cake that begs to be eaten as a mistake. Mistakes make serious eats too.
Rule of thumb is this take into consideration how sweet you like your baked goods and how sweet your liquor of choice is. If you pick a not so sweet liquor still use your vanilla. You are layering flavors.

Milk for everyday, but dark when I want The Good Stuff.

the darker the better...

dark, dark chocolate

Most certainly dark ... milk carries the memory of too many crummy commercial candies.