Hi rugbygirl, I'm t1 and have been cycling regularly and racing the last year. 1st100k is a good milestone. You should work up to it, you'd wanna be able to comfortably do 80k a week before to 100. Sports gels are your new best friend!
they are a great way of keeping your sugars up during the ride without being to hard on the stomach. Personally I cant eat a lot while riding, I find fruits and bars tend to repeat on me so dex sweets and gels do the trick. But trial and error to see what fits for you. I'm currently training for a 200k hill event so I'll gradually increase the distance and severity of each spin till I'm up to speed. Hill repeats are also a good way of increasing strength and conditioning. Hope this helps?