Excellent observations and well written. Everyone will have their opinion, but let's see if I can answer a few.
Re: insulin line, yes that is how it is done. You must be very careful, check and double check, because it is only you. However it is done thousands of times a day with just one nurse throughout the U.S. I never saw an insulin dose-related incident while working in corrections. However, I had my doubts about some of the reports from the inmates about feeling bad after insulin, etc. and the method of injection by the nurse. I saw many poor nursing skills in corrections by nurses who had nothing but contempt for inmates. I would watch them jab the needles straight in and sometimes I was certain that it was being given IM, but no one seemed to care, and I was "just agency". However, it was my experience that the inmates would watch you very closely and they would catch any mistakes before you could make them. It helps to identify one of the bottles by always making sure there is a recognizable difference. For instance, I always put a rubber band around the 70/30 bottle. You will do just fine, you just always have to be alert and precise.
Tell your husband that it is safer on a bad day than the ER is on a regular day. No tripped out, coked-up junkies breaking restraints and taking a swing at you. Bad boys come in, in full leg irons and cuffs. Or at least cuffs, and escorted. For the rest, there should always be a c/o within easy reach.
Seg is always weird, but you will habituate to it. If it doesn't feel weird, then I would worry.
Re: security-there was always a c/o presence at the clinic entrance, making sure that the inmates either had an appointment or a real reason for being there. They would not let just anyone walk in. Your situation may vary, are you behind glass, or is the desk open? I have to leave this to other posters for their opinion and experience.
Re: #6 Well...as I mentioned, I saw some really BAD nursing while I was working in corrections. I found that the bad nurses really don't like a good nurse, especially one that has more education and real skills to come in and make them look bad (which is easy to do, sometimes just by doing your job). The good nurses will applaud and welcome you. Get used to seeing inmates treated like dirt by some of the other nurses and staff. It goes with the territory, so all you can do is be professional.
Re: not feeling scared...I did not feel scared in all the units I worked in. I only had an inmate act as if she would hit me once, and the c/o quickly put her in her place. I dealt mostly with men though, and felt comfortable. You are right, some seem like SUCH nice guys, but we are seeing them drug-free and without the problems they had in the free world. Beware though, because it will shock you when that first really nice guy that you learn to "like" tries to steal a syringe, or something else. They will try to manipulate you, and at first you won't even know you are being played...but it is all part of the process.
Enjoy your job! You like it, and it seems good fit.