halving this recipe in tsp. and cups

Well, I would recommend trying the chart at https://www.kingarthurbaking.com/learn/ingredient-weight-chart
as a good place to start. I don't know what to suggest for the cake crumbs though. That could vary depending on precisely what kind of cake you were using. Maybe you could try using the suggestions for bread crumbs?

I'll be honest with you, it would be far more accurate and more likely to get you the result you want if you stick with the weight measurements. The problem with cup measures is that amounts don't quite match up with weights. A cup of sugar isn't the same weight as a cup of flour, a cup of nuts, etc. When you get to the eggs, then it's a bit easier. The standard weight for a large egg is an average of 2 oz. So your original recipe is asking for roughly a dozen eggs, and half that would be 6. Just out of curiosity, what in the world does this recipe make? I'm thinking some sort of fruit cake or steamed pudding, perhaps?