Hi and welcome to the forum. I’m sorry your kitty has been diagnosed with FD but you have come to the best place to get help.
I'm very glad your vet is going to test for ketones.
When the vet prescribes an insulin ask if you can have either Lantus or Prozinc. Older insulins such as vetsulin is no longer recommended for cats. To treat feline diabetes successfully you need a long acting suitable insulin for cats, low carb food and hometesting the blood glucose to keep your precious kitty safe.
I’ll link
CATCHING AND TESTING URINE.
Here are some useful links for you
Low carb food chart diabetic cats need canned/wet food that is 10% or less carbs. There is no need to feed expensive prescription foods and definitely no dry foods which are too high in carbs.
Hometesting hints and links there is no need to buy a pet meter. A human meter is just as accurate and safe and is much cheaper to run. When you get lancets, get size 26 or 28
Help us help you this has the spreadsheet instructions and how to set up a signature which tells us all about your kitty.plus other useful into including a hypo box. Make sure you get one set up for when insulin is started.
I hope you will keep posting here. This is a wonderful and knowledgeable and supportive community and everyone is happy to help and support you.
Bron