Welcome!
I’m quite new myself, this forum and group is super helpful, you’ll find the appropriate guidance to treat your cat in the best possible manner!
Are you planning on home-testing his/her blood glucose? It is the most secure way to monitor and adjust insulin dose and food intake.
More experienced members will tell you where to look at for what.
You say he’s starting insulin tomorrow, what type of insulin will it be and how many units did the vet recommend to give? My own cat had super high fructosamine at diagnosis and the vet recommended that we start with 3 units, but she never needed so much. It’s best to start lower and increase with home monitoring, you have to avoid hypoglycemia.
Welcome to the Forum, you are in the right track, I was very scare as you when my Corky was diagnosed January 2, 2023 he is also 10 male, I was frantic, Corky had the same symptoms, he grew up since 8 weeks old on MeauMix dry food, he is an inside cat, when I got home from the hospital, he was there for 8 days, I had no idea what to do with all the stuff I was given, Thank God for This Forum, my Corky today, is as healthy as before the diagnose. My secret is as follow: yes the wet food is very important, you do not need prescribed food, Fancy Feast is a very good choice, not only is USA made, regulated, inexpensive, many flavors to choose from, just be sure you pick foods that are between 0-10 % carbs, normally all pates, also is important that you have at hand what it's called a HYPO KIT, this will contain some medium carb foods and high carb foods in case hi's glucose gets lower than 50 ,home testing is very important, especially before shooting insulin which means AMPS/PMPS, you do not want to shoot not knowing his glucose number, most of us members use the ReliON Premier monitor and strips, inexpensive and reliable, if you can post the Lab work, type of insulin, dose, diagnosis, and also create a spreadsheet , so you can monitor his progress and glucose numbers, as well as the Forum and advise you better and give a better input, below I'm also posting several links to look at and learn how to not go crazy, and make you feel more comfortable We are here for you that important thing is to breath in and breath out, any concerns no matter how small reach out to the Forum, you can trust the experienced members to get your baby back to his better self and no concern is a dumb concerns, I learned step by step, I trusted, read everything and did everything I was told, A lot of new members, have had bad experience with
Vets, since they are not familiar with cat diabetes, be patient with yourself, it will all work out, and before you know it you will be a pro



links below, also you can see Corky's spreadsheet by clicking on his name in blue, and scrolling the page to the right you will see his schedule of meals , to get an idea, the links below can help you start, read as many post in the main page FORUM, I also read other post I learn a lot there as well not to panic
https://www.felinediabetes.com/FDMB/threads/dr-pierson-new-food-chart.174147/
https://www.felinediabetes.com/FDMB/threads/how-to-create-a-spreadsheet.241706/
https://www.felinediabetes.com/FDMB/threads/creating-a-fdmb-profile.159626/
https://www.felinediabetes.com/FDMB/threads/how-to-shoot-your-cat.290439/
https://www.felinediabetes.com/FDMB/threads/hometesting-links-and-tips.287/