How kitty feels would depend in large part to where his blood glucose is at. Last thread you posted, you were using Prozinc, but not shooting twice a day in equal amounts, if I remember right. And you were going to have the vet check for other conditions that might explain why the dose has been as high as 5u? Did you find out anything new?
Also, I think you said that pancreatitis had been a problem. Is that still a problem? That makes a cat feel really bad, and can cause a good deal of pain.
It's hard to answer some of your questions relating to how kitty "feels" on insulin. Normally, if the dose is right (not too high or too low) it should make him feel better. But if the dose isn't right, he could be suffering from BG that is too high which makes him feel bad, or too low, which would also make him feel bad. It's hard to tell just from looking, because feeling bad is feeling bad, period.
When Bob was first diagnosed, he felt like total crap. Cried a lot, didn't want to be around me or anyone else including our other cat. Didn't want to eat most of the time, while at other times he would eat anything he could get into because he was literally starving. Didn't want to be petted, cuddled, just wanted to be left alone. But it only took a few days on insulin before he started to improve. It was a couple weeks probably before he stopped drinking like a fish and peeing like a racehorse. His appetite improved once I started feeding him Fancy Feast, and then he stopped acting like he was starving. He got more social too, and started grooming himself again. He still didn't want to play much, and his legs were to weak to jump up on the sofa, but if I picked him up and put him in my lap, he'd stay there as long as I'd let him. It wasn't until weeks later, after he was "off the juice", that he regained the leg muscle needed to jump up on the sofa or bed, and really started to "play" again. His favorite game is "fetch", and he didn't do that for months. I let him decide when he was ready for that, and one day he rewarded me by bringing his "krammie" (that's his toy he fetches) to me and dropping it at my feet and crying for me to toss it. That's the day I really felt he was "better", even though he'd been in remission for months.
Specfically though, to your questions, all I can tell you is how Bob acted.
He didn't sit all hunched after a shot.
He never seemed to have an upset stomach, or at least he never barfed or looked like he wanted to.
He was "hurting" however, yes. That was mostly due to muscle weakness and dehydration. It hurt him to move at all at first.
He was "antisocial" and didn't want to be touched, petted or messed with. That only lasted a few days though.
He still enjoyed stretching out, but it was summer time, so not really in the sun. Mostly over the AC vents on the floor!
He didn't sleep on the sofa because he couldn't get up onto it. Mostly just on the floor or in his cat bed, or in his favorite thing in the world, a cardboard box (had to cut down the sides so he could get into the box).
If the insulin is working, more importantly, if the dose is "right", then yes, he should show improvement on all the things you asked about.
If you aren't home testing, please think really hard about doing so. If the problem is just that his numbers are too high or too low, that's easy to fix, but you need to know what his BG is all day long, not just when the vet checks it.
The supplies can be gotten to home-test for nothing, except the cost of shipping them to you. There's a "sticky" thread at the top of the index page that tells you how to go about getting a home-testing kit. Not only is the safest way to treat diabetes, but it will do so much to help you "know" how he's doing and maybe answer most of your questions.
Carl