It’s very easy to do way too much during your half ironman training, but it’s also quite possible to not do enough.
There is nothing worse than getting to the day of an event knowing that you’re not really well enough prepared to do your best, this is why your training and preparation has to be just right.
You need to gradually increase the distances of everything gradually but progressively up to a week or two before the day of the race. You also need to try a few sessions where you actually practice all three disciplines at the same time in race order. If your half ironman is going to be in open water then you will definitely need to get out in some and get used to how that feels… it’s completely different to swimming in your local indoor pool.