This is a bit long, so read as you're able, I know it's a lot to digest and super stressful at the beginning.
When I first started with Kit, it took me probably a month or longer to get her to settle down even a little for testing - and there were so many tears (from me) and since she's got tortitude in spades, lots of hissing and growling and swatting from her. And it's so stressful, I get that. The more you do it, the more you both get used to it (hopefully). You DH being able to help is amazing - Kit was first diagnosed in 2019 (remission mid 2020), and came out of remission a year ago, and my BF only just in the last month was okay with learning to shoot. He doesn't want to test at all because he's scared he'll hurt her (or vice versa). Her being docile for it, even while not wanting you to do it is such a good thing!
And they pick up on our emotions (which I know are hard to temper in a stressful situation). I talk to her in a soft voice (and now that it's been so long, sometimes a ridiculous silly voice), and sing made up songs to her (which is also not just a shot time thing anymore - I think they're hilarious, she tolerates them begrudgingly).
One thing I remember doing is gently rubbing her ears and touching them at times I wasn't testing her. And treats at shot time can also be a big help if they're treat motivated.
As far as food - there are some basics as Diane mentioned, but every cat is different on when they have their onset and when they nadir. And depending on how in depth you end up getting into it will also affect that. Kit is on TR, because testing her is one thing that I have control over in a somewhat crazy and what feels like slightly out of control life. But also, her food is something that I can control. Because I have the data I have, I know that she likes to do a big ol' drop at +2. So, I've been experimenting since last fall with ways to counteract that drop (big drops can cause bounces, and she likes to get a in a drop/bounce cycle that takes forever to clear). Her schedule is to be fed 2-3% at shot time, 7% at +1, 9% at +1.5, and then whatever I think she needs at +2, +3, +4. Sometimes she doesn't eat past +3, sometimes she'll still have food up to +6. But it all depends on what numbers I see. I also leave her food dishes out until I've decided the time for food has ended. So she'll get food at shot time, probably won't eat it all, but I leave it out so she can come back and graze, because I know she's more of a grazer. But those things will all be reflective of what you notice in your cat. And writing it all down helps so much (my memory is not the most stellar).
I also don't use a feeder (own one, haven't used it). Kit's not super motivated to run to the feeder to eat, so I just haven't done so yet. If you've noticed that she's running to eat at +3, maybe try to get a test then to see what her numbers are like. And if she's dropped lower, maybe feeding at +2.5 is a way to smooth the drop some.
I know it's so stressful right now, but even just being here is means you're doing so great! And it does get easier. As you get more accustomed to the basics, try other things. Even testing some is more than a lot of diabetic cat owners do.
