Ddog was diabetic, he died six years after diagnosis (not related to the diabetes - he was old man by then!).
My advice would be:
Get the prescription from the vet and order canisulin and needles from Animed.
Get a needle clipper to dispose if needles - a few quid on amazon
Food needs to be less than 10% fat dry matter. There is a brilliant Facebook group UK diabetic dogs with info on how to calculate the calories needed for the dog and working out the fat by dry matter. We fed Chappie original which I know gets looked down on but my dog refused to eat the ridiculously expensive Hills food from the vet. He thrived on it and looking at the comps the Chappie came out better anyway. There was an issue which production for a while and we fed Burns white fish. Absolutely no deviation on the food.
inject during feeding, 12 hours apart. It needs to be consistent. If the don’t eat don’t give a full dose, but you can give a basal dose of 25 %.
Get a glucomoter to check glucose levels. This was a nightmare for me as it was from the ear and he HATED it. I only tested when there were symptoms of high or low these include excesff sad I’ve urination, increased drinking, shaking / tremors.
the vet should do a fructosamine test every three months to check for long term glucose levels and adjust dosage if needed.
Blindness. My dog was partially sighted around 8 months after diagnosis and fully lost his sight 18 months after. Cataract surgery is an option but it is intensive, and for a proud terrier like mine wet old have been the wrong decision. He coped brilliantly. Keep the home in the same layout, track commands like up/down for stairs or kerbs etc when out.
I hope that helps, if you have any specific questions let me know.
🐾