Most people who start training for Ultraman events end up overthinking it and spending waaaaaay too much time doing long slow stuff. There is no need to do countless over distance swims, rides and runs.The reality is that for most (unless you want to win it) it isn't much more than Ironman. I'd get your swim worked out as that is the biggest challenge for most and then schedule some long rides and runs somewhere in your training blocks. Same goes for Double,Triple Iron's but with those you need to factor in riding through the night and sleep deprivation

The hardest thing about Ultraman these days is paying for it.