Welcome! Congrats on your impending addition! Oh what fun ya'll are in for.
My condolences to your cat.
I've not much advice, but there are plenty here that have a wealth of knowledge on diet. You might look in the Health and Diet forum.
If ordering food, supplements, treats, etc via the internet is an option, you may want to consider that over cooking for him. It can be very tricky getting the correct balance of protein/fiber/nutrition for these little ones.