I wouldn't have thought dieting to the point of lethargy is healthy... that's called starving and that's not good. Having been anorexic in my teens I am not a fan of dieting... everything in moderation, including moderation for me.
VDOT I think he means he is a Type 2 but on insulin (hence the 1.5 tern his GP uses). Some poorly controlled Type 2 diabetics end up needing insulin which is why the old fashioned way of describing Type 1 as Insulin dependent and Type 2 as non insulin dependent is redundant as that is not always the case with type 2.
It's only 10km, I wouldn't bother with bib shorts or any bike kit and in fact I wouldn't bother with cleats, for such a short distance I would wear the lightest run shoes I have... and even with clipless pedals (if you can't change them to flats), I could cycle 10k.. that way you have no delay at transition.... I have only ever done 1 duathlon (loads of tri's).. but that's what I did... run fast, jump on the bike pedal fast, jump off and run fast again!!
What Dave said... you also need to know (esp if you have done little cycling before given that you don't own a bike), how to go down a hill efficiently, climb efficiently/comfortably, corner efficiently (ie be comfortable RIDING a bike), know how to use gears and brakes, get used to the bike you are using as well. It's not just about sitting spinning your legs. Surely your wife would be more comfortable with you riding 110 miles when you've actually ridden a bike before and not just getting on on race day in amongst crowds of cyclists.
p.s. You are an adult, you don't have to do everything your wife says. Buy a bike and get out on it. (Get fitted for it first, make sure it's semi-decent if you are planning an IM).