When you visit the Vets quiz them as to specific steps that can be taken for the chronic kidney failure. For example one of the contributing factors for poor appetite in kidney failure is the subsequent development of ulcers. Use of surfactants such as Sucralfate can protect the stomach from irritation, and also serve as a phosphorous binder. Not only is a low protein (hydrolyzed) diet important but also a low phosphorous diet. If it were my puppy, I'd have it on Hills k/d, until the BUN and Creatinine values were lowered. Then if you wanted to give a home cooked diet, consult a Vet nutritionist. You can give up on the idea of feeding raw and being able to control the protein/phosphorous levels. Fish oil is good, Flax oil is bad. You are wise in holding off on any other supplements. Also ask the Vets about an ACE inhibitor. Sometimes lowering blood pressure helps the kidneys function better.

The liver elevated enzymes could have been due to prolonged use of the NSAIDs for arthritis(?), and may go back down in time. Liver problems also will affect the appetite. This is assuming no other cause.

If the hind end turns out to be vestibular disease, then recovery would be slow over a few weeks of time. It doesn't take too long off feed for an older dog to become weak. So anorexia isn't helping the hind legs.

Probably if you can get the kidney disease stabilized, puppy eating, then the other two problems will lessen. Hopefully any additional ultrasounds or other tests will not reveal any other underlying causes.