All of the PT cats I know about are neutered. My Filou and Tigris are 9 years old and are neutered since they were 6 months/9 months respectively.
Tigris this last year developped an iFLUTD (idiopathic .....). He got prednisone (to keep the inflammation down) and antibiotics (against the bacteria infection he had on top of the basic inflammation of his urethra. He has no stones so he doesn't need a special diet.

The main issue for him is drinking so that the urinary tract is rinsed all the time. As he doesn't love that too much (neither chicken broth nor thinned cat milk) I add a tea spoon full of water to his soft food- now he pees purrfectly!

I don't think you have to feed Felix that food in advance. It could happen if he had crystals (there are struvite and oxalate)- but he hasn't I think.