We weren't educated at all about IUDs at school, bearing in mind I'm 22 so it wasn't even that long ago! They only ever talked about condoms, the implant, and the pill.
I only had my mirena fitted as the doctor recommended it to treat endometriosis, otherwise I never would have done it as the thought of it terrified me. They used local anaesthetic for my fitting but I still found it incredibly painful, and I did pass out afterwards. I took co-codamol and ibuprofen beforehand but it didn't seem to make a difference for me. My pain tolerance is very high in other areas but I have always been very sensitive down there, can't stand speculums or any form of internal examination, so that may have had something to do with it. Also, as I mentioned earlier my coil never settled and I could always feel it inside me, but they did say that my uterus was on the small side when they measured it during the fitting. If you've had children this shouldn't be a problem for you. :)
My best advice would be to definitely take someone with you, and don't drive yourself. You might be absolutely fine, especially as you've had children now, but just in case you do feel a bit woozy afterwards. Apparently the anaesthetic injection is a lot more effective than the gel, so perhaps ask about that too if you're worried about pain. I don't mean to scare you at all, in fact I'm the only person out of my group of friends who had a bad experience with it, the rest were all fine, so hopefully things go well for you :)
You can absolutely have the coil removed if you're not happy with it, you don't have to wait 5-10 years. Unfortunately some GPs are stubborn and refuse to do it but if that's the case I think the GUM clinics do it. The removal is a lot quicker and much less painful than the insertion.
Good luck! Xxx