I can't tell where you are, so I won't make a recommendation on Vets.
Have one of the Vet Technicians show you how to do the subcutaneous
injections - have them watch YOU do it.
(I had to do this for two cats, the first vet just said "here's the stuff",
demonstrated & that was it .  as a result, it was
generally a disaster.  The second time I insisted that I do it while the
Vet/Tech monitored and corrected me - went MUCH better)
I don't know how your cat will react to it, but my cat actually perferred
the Purina NF dry food - she wasn't very fond of the canned stuff.
The only problem we had was that my cat would get very loose stools, BUT
that may have been the result of a fibroid sarcoma tumor she had that the
vets missed & which resulted in the amputation of her hind leg.

The problem with this diagnosis of "mild renal failure" is that it isn't
real firm - my cat was so diagnosed, but the diagnosis was based upon an
increased creatinine level.  We had her on NF and the creatinine level
dropped to normal, as did the BUN - bottom line is that increased creatinine
level MAY (but not always) be caused by an underlying infection (in my cat's
case it seems to have been - because after the cancer removal, the levels
remained normal for a number of months - but then the kidney failure (which
is NOT uncommon in cats) kicked back in. ((incidentally she was 18 yrs old
when she died)).

I'll be happy to share any information I can.

Yes indeed, we have had experience with what you are going through.  Our
Turkish Angora, also 8 yrs old was diagnosed with kidney failure and in
order for him to continue a normal life, the Vet had us (me) to inject 100
to 125 ml of Lactated Ringers.  At the same time, we had to give him
Potassium orally with a syringe ...forgot the dosage.  I went through that
routine with "Sugar" (his name) for 17 months.  In his last days, we started
to notice blood on his white fur just after he would pee, took him to the
Vet ...he didn't want to suggest that we put Sugar down but his diagnosis
was that Sugar was getting in a fatal state for which he could be in pain.
After three days and noticing a big slow down, we decided to put him at
peace, that was in June 2002.  When I started Sugar on his medication, it
took about a month before he realized it was going to be on a daily basis.
Sugar had his medication spot in the same location in our house and RV, he
knew when being placed in that spot what to expect.  Most all was done in a
wide window sill in our family room, it was about 4-1/2 foot off the floor,
had a plant hanger hook on the ceiling for the Lactated Ringers bag. That
window sill afforded the perfect place to work because of being at arm level
and I could easily keep total control.  As for leakage with the injection,
it was noticeable but quite minimal and never created a problem. Throughout
the time, Sugar was quite easy to work with and hardly ever tried to get
away.  If I wanted him to stay on that window sill while making
preparations, to answer the phone, etc., he would ...but believe me, he
never but never wanted to go in that spot for anything else.

With your email address, I have a feeling that you are close to us ...we are
in Bremerton, just across the sound from Seattle.  If your email address is
good, then you will be receiving our phone number ...would like to have a
chat with you on the subject.

May your cat have a long life.

Rich & Zara

I'm sorry I can't help as when my cat was diagnosed with kidney
failure he was already well on the way,Idont know why they didn't
catch it sooner, twice they told me he had a bad tooth, so he finished up
having two teeth out[almost a &100 each] and when they did diagnose it
they never offered me any treatment,so I assumed he was too far gone,
I just had to wait the vets said I would know when it was time.I just
wish I'd had a group like this to talk it over with, but I didn't have a
computer
then, he died in 200 aged 13 -1\2.wherever he is he knows he's still
my Baby,.  Jean P.