I've been interested in triathlons for a while now, and I'm starting to train for my first sprint (actual race TBD). However, I'm starting out at an obese weight. I'm currently 1.88m tall (6'2") and 120kg (265 lbs). I hope to be somewhere near 110kg (240lbs) before I try a sprint, and closer to 90kg (200lbs) before doing an Olympic or half Ironman. There are a couple things I cant quite figure out based on reading alone:

1. Should my process change when a calorie deficit is the goal? Everything I read about training says to fuel the work and replace the calories you consume. I obviously don't want to do that because I have 10+ years of excess calories sitting inside of me that need to be used. Has anyone had success with training on a deficit? How low have you gotten while still making progress towards both goals?
2. Because I'm heavier, I'm concerned about injuries. Luckily, I can run at a snail's pace for an hour without any discomfort or issues, but the threat of a nagging achilles or knee worries me when I start to ramp up. Additionally, I have a road bike, but I don't even think most road bikes are made for my weight.

If you accomplished this (lost significant weight while training), how did you handle the deficit and prevent injuries? What worked?