It's a long time since I made a Black Forest Cake, but I have made a few and eaten more. Always sponge of some kind, I think the last one I made was genoise sponge. I'd expect a more dense chocolate cake would be a bit too rich and heavy when assembled.
I like kirsch, and have a bottle I bought in Germany about 10 years ago, but I only use it in cooking, though it is drunk from little thimble glasses with coffee after dinner. I agree with Fyretigger, you don't need kirch, rum is a good sub, or grape brandy, but if possible stick with spirit rather than sweet liqueur. The name Kirschtorte comes from the cherries (Kirschen) rather than the liqueur
Dont know what's available where you live but I have made with a jar of cherries in booze infused syrup, which is a good shortcut