The usual ratio of almond cream to pastry cream is 2/3 almond cream to 1/3 pastry cream.
You can use frangipane in any recipe that uses almond cream and vice versa, it's just a question of taste.
As with almond cream, you can store it in a sealed container in the fridge for a few days, but it also freezes well. You can then take only the quantity you need for your recipe from the container in the freezer.