You won't need to carry anything if don't want to, we all did the same with a big storage box for food/spare gear etc and just pick stuff up each lap. Quite nice running an ultra without having to lug around loads of kit all day.
Thanks for reading my report Hardcastle 24 is a really great little race and the support is very friendly too.
The course is quite tough to plod around for such a long time but it's beautiful (and it does have flat and downhill bits too!) so just take it easy and keep on plodding and you'll definitely get through 100k in 24h!
Make sure you've got plenty of batteries for your headtorch, it's pitch black on most of the course when night falls.
I think there's some value in doing one long (30ish miles) run at some point in your schedule because it's a good opportunity to spend time on your feet and to practice the other aspects of a long days running such as planning an eating strategy and hydration and carrying a race pack etc but generally I'd probably stick to a couple of 20 milers as the longest runs in training.
I know what you mean about family commitments, I sometimes look on jealously at people who seem to have unlimited time to spend in the hills every week when I'm plodding the long way to work on a rainy morning but I guess running and life balance are vitally important too