I would start with 4 tomatoes for 1 jalapeno or chili. The spices are all about 1 tablespoon. After that I just go by taste. I always taste it after I blend it to see if it tastes right. If its not 'mexican' enough that is the cumin. You can usually tell if you have added enough garlic and onion powder. Dependng on the blender and how you like the salsa it might come out runny so it could take a few different batches to figure out how you like it.
I will put this with eggs and cheese for breakfast and the old cookbook has a recipe for breakfast caserole that calls for salsa. Its good on mini pizzas made with tortillas and any meat.
Let me know how it turns out!
Another thing allowed on plan is Frank's Hot Sauce. Its great if you like buffalo wing flavored sauce. I make nuggets with it. I think the recipe is in the thread. Ver good.