We all get nervous about our kitties going low. Home testing is the best way to keep him safe, so you're on the right track!
Here's a little to-do list for how this works:
1. No food for two hours before each dose. Food impacts the blood glucose (BG) numbers, and you need to know what the numbers are without that influence.
2. Get a BG test
before each dose. We call that AMPS (a.m. pre-shot) and PMPS (p.m. pre-shot) Those two tests are "required." If you get a pre-shot number that is below 200, don't give insulin (that will change as you get more data, but for now follow that)
3. The order of things is test/feed/shoot. Test first, then give food, then give the shot. If your kitty doesn't eat, then giving a shot can carry a risk, so make sure he's eating. Doesn't have to be a lot, just a tablespoon or so. More is fine.
4. When you can, get mid-cycle tests. The usual nadir (lowest BG point) for a cat on prozinc is +5-+7 (five to seven hours after the shot). However, some cats are earlier or later. The curve will help you figure that out, although it can shift.
Transitioning food carefully is important. If you go from high carb food to low carb food, some cats will drop as much as 100 points almost overnight. So since you're on a high carb food, and just barely starting insulin, you're going to want to transition carefully. So start with a little new food, then a little more new food, then half new food, and then more and more until you're all the way to the new food. And don't begin that transition until you're comfortable with testing because it may require some adjustment in dose fairly quickly.
As far as the curve...you can do that at home for free. Many vets will insist on an in-office curve, and it's not my intent to get you in a fight with your vet. Here is the thing though: getting a curve in the vet's office will most often result in false high numbers. When a cat is stressed, their numbers go up. So then most vets will suggest a dose based on the numbers they see in the office which might be a lot higher than the numbers you'll see at home (hopefully your vet won't do that, but we see it a lot here). So go ahead and get the curve done (and make sure the vet gives you the numbers so you can see when the nadir is), but please please please don't increase the dose. Especially not before you've completed the food transition.
For now, get comfortable with testing, transition the food, and then if your home numbers indicate a need, consider changing the dose.
And I share this in the hope that it will help you feel more comfortable and prepared, so please don't let it scare you! It's links to information about what you need and what to do just in case your kitty does go too low. By the way, too low on a human meter is below 50:
http://www.felinediabetes.com/FDMB/threads/hypo-links-be-prepared-just-in-case.48385/