There is some scary stuff to learn about with FD. Comas and low numbers are frightening, but the good news is that since you're testing, it's less likely to happen. And if it does, you can catch it and we can talk you through it. We've had plenty of members here hit some low numbers and there is usually SOMEONE around to hold your hand/walk you through what to do/remind you to make coffee and eat some chocolate. If you do hit a low number, post on the Main forum as well as here with that red 911 and you'll get eyes pretty fast...and we won't hesitate to tell you to go to a vet if we think it's needed. I can tell you I've seen plenty of hypos or near hypos on here and hardly ever have they needed a vet...only if a double shot was given accidentally or something like that usually. Have you got a hypo kit prepared? That made me feel better because I knew I was ready. Had high carb food, karo syrup, extra test strips (change those out every so often), coffee grounds (I wasn't kidding about the coffee!), a bar of chocolate (nope, wasn't joking about that either...you'll deserve it!), and the hypo instructions printed out + the number and name of the closest emergency vet and my vet. That way, you're ready and you won't be rushing around looking for stuff if you need it. I will say it again though...it's RARE that it's bad. 50 is the take action number but that's not even really hypo...that's just where we start doing something to make sure it doesn't BECOME one. And we'll help you if one hits...or someone on Main will.
Ketones. Yeah, they're scary. And honestly, they scare me more than hypos. I've never seen a cat on here die from a hypo but I have from DKA. And it's heartbreaking. But they too CAN be dealt with! The earlier you catch them the better, so make sure you're testing. You can use urine strips for humans...ask at the pharmacy and they can point you to them. Sounds hard, but catching urine isn't too tough...we have several tricks if you need.

The recipe for DKA (diabetic ketoacidosis) is not eating + not enough insulin + some sort of infection. It can happen at lower numbers or when those things aren't present, but you're most likely to see it then and in higher numbers. So test for ketones when you can, but don't worry about them unless he starts acting off and refuses food. Then you want to test ASAP or just take him in if you can't get a test. We've seen PLENTY of kitties recover from DKA and go on to live long lives and be healthy. We've also seen PLENTY of kitties (including mine!) who never got ketones...yes it can happen, but if it does, we can help you (and we really won't hesitate to recommend a vet for that one) and we can help you prevent it by more aggressive dosing in the future. It's more likely that it won't happen without some sort of cause, and if you're testing you don't have to worry because you'll catch it fast and the recovery will be that much easier. One thing about the ketone test strips...check them at EXACTLY the time listed on the bottle (I think 15 sec). They get darker over time so you'll panic if you wait and check it later.
Okay, that was longer than I intended, but I wanted to give you a rundown of both things you mentioned so hopefully you wouldn't be as scared of them...I find knowledge to be power. Both those conditions CAN be dealt with, sometimes at home, sometimes at a vet, and we can help you prevent/recover from them if they do happen. And you might never deal with either one....but if you do we can and WILL help you.
Please ask everything you want to. No dumb questions here, and we get the fears very much! I hope my novel here helped some and didn't scare you.

Let me know if we can clarify any further and be secure that you are NOT alone.