Having done IW, I can tell you the swim is not bad as long as you're comfortable in cold water. I swam it in a shorty wet suit. Took a couple minutes to get comfortable, but once there, I did just fine.

The bike course is actually fairly easy for that distance. The biggest challenge with the bike course (so long as it hasn't changed since I did it a couple years ago) is that it finishes going up hill. It's not a bad incline but about the last 3-4 miles is up a couple degrees and you're legs are already spent. If you know this and pace yourself for it, you should be fine. Just don't get fooled early and blow up at the end.

For me, the biggest challenge was the run. I forget if they call it flat or rolling, but they're bald face liars. It's hilly. Not like big hills, but it's a crap ton of up and down. Most of the run course is on a golf course and we've all seen how those things are laid out. You can go up 10 feet and down 10 feet a dozen times in a half mile. I got it done with time to spare but man, was I sore the rest of the day and all the next.

Just stay in shape for an Oly. If you can do an Oly, you're physically fit enough for a 70.3. At that point, the two biggest challenges is going to be pacing yourself so you have gas in the tank for the whole day and nailing down your nutrition/hydration strategy.