Limewave, I believe that you can do it. But I also feel like I need to make sure that you've done your reality check.
Most of the people I know train about 300 to 600 hours for a HIM distance race. I am usually traing for 13 to 18 hours per week for that distance.
Is your back OK? Do you feel like your body can take it. 13 miles running after 56 miles on a bike is tough on the system and you'll be out there for anywhere from 5 to 7 hours in total.
Finally, your DH is worried for a reason and it does have to do with control but not in a bad way. If you decide to race he will have no way to help you if you are in trouble. My DH gets way more anxious before my races than I do. One time I asked him why and he said it was because he can't make the decision for me of whether or not I should go on. His arguement was that if things were going south and I wasn't functioning well, he had no ability to influence my decision to stop and as stubborn as I am, that was a very scary prospect for him. So before I race we go over the game plan, I reassure him of my decision making process. Eg - I will stop if I start seeing double....
You can also not sign up for the race and just start to train and agree that if it becomes too much you'll back off but if you're handling the training load well by _________ date before the race, then you'll sign up.
Be sensitive to your sweetheart, he means well, they're hard wired to want to protect us. And be honest with yourself. I truly believe you can do it but you have to know what you're up for, especailly since you're a relatively new mom.
Living life like there's no tomorrow.
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2007 Look Dura Ace
2010 Custom Tonic cross with discs, SRAM
2012 Moots YBB 2 x 10 Shimano XTR
2014 Soma B-Side SS