Welcome! You are in the best place you hoped to never be in. My boy Willie was diagnosed in early December, and I can promise you that it does get so much easier. I see you are on board for home testing and low carb foods... you're already two steps ahead! Which insulin is your vet prescribing? We have insulin support groups for the various insulins that have valuable information as well, so be sure to read up there!
Couple newbie tips:
1. You don't need a vet prescribed food or even a fancy pants brand. Most folks here use Fancy Feast Classics, Friskies, Special Kitty (Walmart) and Sophisticat (PetSmart), all of which are significantly cheaper and are better quality than what you would get from the vet.
2. You don't need a fancy meter either. Lots of people here use the Relion Micro or Confirm. It is a Walmart product. The meter costs $9, and strips are $12 for 20 or $20 for 50, so they are quite affordable. Target and the drugstores also have house brand meters that are relatively inexpensive. It is good to have a meter where you can get inexpensive strips in the middle of the night if needed!
3. When doing home testing, you'll be poking the ears alot. It takes time to "train" them to bleed well, so don't get discouraged. You'll need lancets (some will come with your meter, along with a lancet pen you can use for poking). The higher the gauge number on the lancet, the thinner the needle. I'd suggest getting some lancets that are 30 gauge or lower... I'd even start with a 28. The thicker needle end will give you better blood flow. Also, the rice sock trick in the stickies was a big help for us.
4. You'll want to get a test before giving each shot, before you give food. You should also be withholding food 2 hours before the shot so that your preshot number isn't inflated by food. You need to know that it is safe to give the dose, and having food out of that equation will let you do that. You should also try to get in periodic spot checks so you can begin to see how the insulin is affecting your cat. Where they hit their low point in the cycle will depend on the insulin and the cat. As we say, ECID (every cat is different). Eventually, you'll want to get in a curve as well, which is generally testing preshot, then every two hours until the next preshot. I'd focus on figuring things out and letting the insulin settle in before worrying too much about getting one in.
5. When picking up your meter, also pick up some ketone sticks. Testing for ketones is important, as their presence can indicate a risk of DKA, diabetic ketoacidosis, which is a very dangerous, and often deadly condition. Surviving a DKA attack is an extremely expensive endeavor, so the $15 for the bottle of strips is money very well spent. It is best to get some fresh urine on the stick... there are tips here in the stickies on how to do that. When starting out, you should test for ketones regularly and if you get any sort of ketone reading, call your vet and ask questions here as well.
The folks here have been angels to us... we've had some really negative vet experiences, and I've placed Willie's well-being in their hands more than once. I literally trust our family here with his life.
Let us know what insulin you're using and we can give you some more specific advice as well... and most of all, welcome!
Here's how I do it: I have a small litter box that's just for ketostix testing. The regular box has clumping litter, so the urine will immediately absorb. I put non-absorbant litter in the little box and put it next to his regular box. Then I put a piece of plastic over his regular box because he won't go in it with the plastic (you could also just remove the regular box). He usually pees right after dinner, so I set it up then and hopefully won't have to wait too long. Once he does his business I just tip the box slightly so the urine pools at the edge and dip the strip in.