I often have to edit recipes due to my husband's health condition, so here is my 2 cents. When you sub applesauce for oil baked goods don't brown as well. You might try cutting the recipe back to 2 T of oil and possibly substituting butter buds for the butter. Of course it won't taste as good, but you would have a lower fat version. Hope that helps.
I've been doing a lot of vegan cooking lately and not had too much trouble with substituting butter with margarine.. just be sure to check the trans-fat levels.. the harder the margarine at room temp, the worse it is for you.. I've been using Earth Balance and it's been working great.
And instead of replacing the oil with applesauce I'd go with one of the less unhealthy oils that can withstand heat (studies are showing some oils become toxic at high temperatures). But the applesauce could still be used to replace the yolk-- a tablespoon or two of applesauce should do it I would think.
and using water instead of milk or cream in the icing would cut out a few calories and grams of fat too.. I use water and powdered sugar to decorate my coffee cakes, and add just a dash of vanilla for some extra flavor.
and replacing the sugar in the dough with sucrolose would also help, but I think it makes things bake a little faster so you may want to keep a closer eye on it...