Need advice for cat with failing kidneys

My oldest cat, Crumbs, is 17 and her kidneys are not what they used to be. The vet says she's doing well, it's progressing very slowly, but that Crumbs has reached the point where she should be on a prescription diet. This is my first time dealing with kidney problems and I've done a lot of reading about it, but I would like to know what other people have done for their cats. Do you think the prescription diets are helpful? What about supplements? Low protein diet or not?

For now, I've switched her to an all wet diet (she used to eat mainly dry) and I'm mixing Hill's k/d with other foods that are relatively low in phosphorus but have normal protein levels. She likes this just fine, although she won't eat very much at a time and needs frequent meals. If I wait too long to feed her she'll vomit clear liquid/foam, or just refuse to eat until she's eaten some grass and thrown it up.

My cat's kidneys are failing. But she has other issues as well, liver tumour for one, so what I feed might not be relative to your cat. I feed k/d wet mixed into what I hope are low phosphorus wet  foods. She will not eat k/d wet straight, and it is important that she eat, so I do the best I can. My vet was adamant that I get as much k/d into her as possible. I try for a 50/50 mix, but don't always achieve that. I offer and she refuses, so I'll toss the food and give her a 70/30 low phos / k/d ratio. At this stage, we are happy that she eats even some of the k/d, but we will soon be coming to the stage where she can eat whatever she wants. She also eats in small meals, but always has. The throwing of stomach acid, frequently with hair, is usually early morning so I've started leaving out a bit of k/d (and thyroid) kibble late at night and giving her a few pieces of kibble during the night if my own bladder has woken me up. I'm not awake enough to go down to the kitchen and make up a plate of food. This hasn't helped with the early morning vomitting, but it does get a bit more of the medicated food into her. The ratio of wet to dry is apron 90/10.

After doing some reading, I opted to sit on the fence regarding high/low protein. Even though, with stage 3 kidney failure, she should be on a low protein diet according to the Tanya site. She gets the low protein k/d mainly for the supportive meds in it, AND low phosphorus  / high protein mixed in. She also get a tonic that contains amino acids, so I'm not too worried that she's missing or low amino-acid wise. Also, I have an aversion to k/d dry after I watched as my neighbour's cat who was fed nothing else after going into sudden kidney failure. The neighbours spent a lot of money at the emergency vet over the course of a week getting the cat back on her feet, and then the cat was sent home with k/d dry and was told it was important that she always have access to water. The owner's decided that they did not want to spend any more money on this cat, and feeding low protein k/d dry would have to be enough. It was a cat that one of their children had stuck them with, and they never fell "in love" with her. They decided on no other supportive measures. I watched her become skinnier and skinnier until she was a rack of bones and wouldn't move from the couch. (IMO, the low protein k/d dry was not enough to sustain her and she should have been fed wet and should have been given supportive measures such as sub-q).

I don't know if all this is helpful to you or not, or if what I'm doing is the right way to go about it, but it's all I can offer from my own experience. What to feed is so complicated.

Edit: forgot to mention that she's getting aprox 100 ml sub-q daily. She's also getting human-grade probiotics.