Half IM to Full

I have a lot of thoughts and will share later.

From my experience (10 halfs, 2 fulls), HIM and IM are completely different beasts and are not even in the same ballpark from a preparation standpoint to endurance, execution, nutrition, and pacing.  You can do a bit of faking in a half, and still put together a semi decent day.  In an IM, when things go south, they tend to go far south and the day can get very long, and all for one simple nutrition/execution/pacing error.

I'd venture to say most people going into their first IM have not run a 26.2 in any situation, including me.  Not that I'd call either of my IM runs "running" by any stretch. 

I think having 2 or 3 halfs under your belt will start to give you an idea.   And sounds like you have sufficient cycling base.  Your swimming comment makes me a little concerned, it sets the tone for the rest of the day.  But you have a year to train it, assuming you do.  I wouldn't take that part lightly.  You should start the bike feeling as if the swim was a nice warmup, rather than having burned a book of matches in the water (which you will not get back).

I did Whistler 2013 and can't recommend it highly enough, simply a fantastic race and venue all around.  If you want a WTC event, that is.  I did Arizona as well, no comparison. 

Ironman finishers have done their first race with a lot more and a lot less experience than you describe.  Having two or even three HIMs under your belt would be better than average.  I had two and the second was a planned race prior to my actual Ironman.  I also wouldn't worry about running an open marathon prior to your first IM (I didn't) as they are completely different animals.  I felt like the IM marathon was more like "26x1mile" intervals.

I have only done Arizona and thought it was a great "first timer" race:  relatively easy course with great crowds.  You need to factor in location, potential weather scenarios, course difficulty, your strengths/weaknesses and room for improvement, and timing when choosing your race.  Arizona checked off all of my boxes/concerns.  Find a great training plan or coach, follow it diligently, improve your swimming with lessons if needed, and show up at the starting line as healthy as possible. 

Like the other poster stated -- you'll have a decent base of endurance and experience if you choose to tackle the IM distance.

IM and HIM plans aren't all that different.  There's some obvious exceptions with some longer rides and runs but for the most part the day-to-day workouts are pretty much the same.   The real important concept to wrap your head around is that it's the culmination of all your training and the overall accumulated training stress that matters much more than any one or two workouts during a given training week.

I swim 4x per week, bike 4x per week and run 5x per week.  The only difference between my HIM and IM plans is that one of my swim, one of my bike, and one of my run workouts will be a little bit longer for my IM training than for my HIM training.  So 10 of my 13 workouts would basically be identical.

The execution of the two race distances is very different, especially regarding pacing and nutrition.  The bike portion of the IM is the glue that holds your day together.  Screw up your bike execution and you're in for a very long and miserable day.  That's certainly an issue at the HIM distance as well but there's more margin for error at the HIM distance.  Chris was spot on when he said you can't fake your way through an IM if you really want to perform well.

You have two of the greatest IM's in the world in Canada with IM Canada (Whistler) and IM Mont-Tremblant.  I did Whistler last year and loved it.  Tough bike and run course but an awesome race.  I'm going back again this year.  Mont-Tremblant gets rave reviews and I'm finally doing it this year.

one additional thing, don't freak out so much that you have to get every element right.  Do your best in training to prepare for what you think you will need nutrition-wise, get your pacing down as best you can.  As GMAN said, IM training is not about one specific workout, but the aggregate effect of 3-4 months of workouts.   So one missed run isn't going to affect your day at all.

do NOT forget to have fun, and be grateful for the ability to be out there doing that, not everyone can.  And don't sweat over things you can't control.  I can almost guarantee that if something goes wrong on race day (and something probably will ), it's probably going to be something you never anticipated.  So the key is rolling with the punches, ad libbing on the fly and adjusting your plan, and always moving forward using whatever reason you have to finish the stupid thing (and you will need a reason somewhere out there to go on, even though it hurts). 

Darn, now I want to do one....

In all fairness, your training for IM and HIM are much different due to your commitment to the training and not so much the difference in a well designed HIM vs IM training plan.

I think the OP was curious as to whether or not there were vast differences in HIM vs IM training plans and the answer is not really.  There are certainly differences but nothing I would call drastic.