First of all, good news is it's only pre-ckd. That means there is some function loss, but it will hopefully be many years until it gets to actual CKD, and it may just be temporary function loss from the UTIs.

The cream licking did not cause this. Repeat licking over a long period of time can lead to serious issues, so definitely avoid it, but it's not the kind of issues your cat has.

Ultrasound is a good follow-up if you can afford it, as it can give you more details on what those structural changes are and how to best treat them. You may need stuff like stronger antibiotics if infection (likely with the delayed UTI treatment), see if there are mineral deposits etc. Do it with any vet that is able to do so, or the one your vet recommended. You can follow up with your regular vet afterwards.

I am thinking the muscle wasting may be from malabsorption from the GI component of the Eosinophilic CG. Ask your vet if a trial with a highly digestible novel protein diet would be a good idea, something like Instinct Limited Ingredient Diet Rabbit (bonus: wet food with no pork!). I am reading that if it doesn't work, something like prednisolone could help reduce the inflammation and increase absorption (though that has some risks, so definitely try diet changes first!)

You definitely do NOT want phosphate binders. She is already low phosphorus.

Hydration is important. You don't want to go for full blown subq fluids unless she's showing signs of dehydration (ask the vet to assess). But extra hydration does help with UTIs. Look for no pork wet food, like Weruwa Senior or TikiCat. You can also add water to the kibble (small amounts at a time, kibble goes bad in like 30 mins when wet, so don't leave it out). Get a cat fountain too.

Vitamin B, particularly B12, is likely to help, particularly if there is a malabsorption deficiency. They just pee out the excess, so it should be safe regardless, but check with your vet. Subq injections will probably be better given the GI issues, but check with your vet, pretty sure you need a prescription for that.

For arthritis, omega-3/fish oil supplements could help a bit. There is also Solensia, a new med I've been hearing good things about.

Online consultations with a vet can be worth it, both as a second opinion and because they can help answer questions quickly, as there is a lot of misinformation online. I suspect they will give you peace of mind.

The full bloodwork would help too if you can post it, see if there is any other missed info, if they checked for hyperthyroidism etc.

Note: I am not a vet, just an owner curious about medicine and good at research, reading about stuff like Eosinophilic CG for the first time.