You can cook in whey instead of water (or mix it with water), if you are making quinoa, for example, or rice. Also, you can substitute it for milk in certain recipes, like quiches. Just be mindful of the amount of spices you are adding, b/c whey tends to be already a bit salty and you may need less salt than what the recipe calls for. You can add it to soups and marinate meats in it... You can also make homemade ketchup with yogurt whey... don't remember the recipe off the top of my head, but let me know if you want it and I will find it. Or I am sure you can just google it too.
That's all I've been using it for.
Also, I have never heard of making ricotta with whey... but I made it using raw milk in the past.
Your pressure cooker looks very cool, I've never used one. I make yogurt only using a pot. I am sure the pressure cooker makes it easier.