RAI is actually the only treatment I didn't do, so can't help you there, but maybe I can offer some insight from my experiences. I was on methimazole for four years and did pretty well on it. My only issue was a TSH that remained suppressed, but my T4 and T3 were pretty stable. My dose for the last 3 years went from 10 mg down to 5 mg daily, but for about 2 1/2 years in the middle I was alternating 10 and 5 mg. I would have been comfortable remaining on methimazole longer if I hadn't developed a nodule.
My nodule was pretty big. It was a type of tumor that can't be diagnosed without removing it, but the very size of it made it more likely to be cancer. If it had been malignant, I would have ended up having RAI several weeks after my surgery, but fortunately it was benign. I know you asked about RAI, but if you ever have questions about TT, I'd be happy to answer them. I had an excellent surgeon and my TT went perfectly with no complications in spite of the fact that it was extra challenging due to the size of my nodule (7cm) and location (growing down past my collar bone). I've had other surgeries and my TT was so easy in comparison!
Regarding life without a thyroid: It's a little scary to know that I'm totally dependent on a pill for my thyroid hormone, so I try not to think about it.
I'm actually better about taking my levothyroxine than I am my other meds. I take my other meds mid-morning whenever I think about it, but you have to take levothyroxine on an empty stomach, at least an hour before eating or taking other meds. Most people take their levo when they wake up in the morning. I tend to wake up very early (between 4:00 and 6:00) every morning and then fall back asleep, so I take mine then. When you take such a crucial medication at a time when you're half asleep, you can't afford to make mistakes so I think most people use a pill sorter for their levothyroxine even though it's just one pill.