I went from couch to Ironman finisher in less than a year.
First, I’d plan on doing the full Ironman. There’s a big difference in atmosphere and feeling of accomplishment of a full compared to the half. I signed up for a 70.3 (St George) and then did the full (CdA) a few months later. The 70.3 was good preparation, but the full is an entirely different level of difficulty. It was 108F that day and several people didn’t finish. The full was brutal.
My typical training week for the last few months was waking up at 4:30 and going to swim practice for an hour, then I’d ride my bike to and from work (30 mile round trip), and then a 4-5 mile run. Friday nights I’d run a half marathon and then Saturday I’d go for a long bike ride (did 100 miles twice) and do a 1-2 mile swim in the river. It’s a big sacrifice and your wife needs to be on board. We actually met a few people at the Ironman race that were divorced or soon to be divorced. That’s why I only did it once.
By far the biggest bang for your buck in training is the bike. You just have to survive the swim and hopefully you have something left in the tank after the bike to run part of the marathon.
You’ll remember crossing that finish line for the rest of your life. Good luck! Learn nutrition and how your body reacts after long distances!