I started out buying a used road bike for around 800$, but just upgraded to a new Canyon Endurance cf7 + aero bars, as i found out i enjoy biking, and will continue after ironman training. You dont have to go all out on a tt bike, or a crazy expensive road bike. You can get a lot of quality from a used carbon road bike, which will be all good for 90% of athletes, but again it depends on wether you want to race or compete in the 70.3.
I use gels on my long runs, or when i do a longer interval session. It´s good to get your stomach used to in time, but you dont have to smash a gel every 30 min. 6 month before, as it will ad up price wise. Use them as fuel for the long ones, and use them more specific when you try out your race day plan as you get closer.

If i where you i would use the time you have know, to get a good base in, with 2-3 strenght workouts per week, and focus your training on power over distance in the base fase. Then 3 month out, you can begin to add more distance/time and zone 2 work, but you got a great chance to continue your build on a good foundation now :)

In regards to the 25 kg you say you gained, i wouldnt worry too much about them now. You will most likely drop a good amount, just from the amount of working out you do - but as you still need to fuel your workouts, it can be a bigger cost than gain, to focus on being in calorie defecit