Use a strong black tea here (think Assam or English breakfast tea). If you're a little weary of the tea leaves: they're pretty tame, I promise. They add some chew but that's all. If you really don't want tea leaves in your cake, steap the tea in the milk for 30 minutes, then discard the tea leaves.
You can use one 9" round cake pan (bake at 350F for 30-40 min) or make cupcakes (bake at 350F for 18-22 min) instead of using two 6" round cake pans.
The Kahlua is pretty subtle here; if you want it more prominent/boozy, feel free to poke the cake all over with a toothpick, and drizzle 1-2 T Kahlua over each cake layer before you layer and frost the cake.
There's a pretty minimal amount of frosting here; feel free to make 1.5 (or even 2) times the amount here if you want a higher frosting to cake ratio.