Ok. I’ll try to answer your questions . . .
That depends on your fitness base. I’m 61 and came into TR about 6 months ago with an average weekly TSS in the 600s so the prescribed workouts were too low so I did the +1, +2, etc versions to make them hard. My typical SS workouts are 1:30-2:30 and daily TSS from these workouts would increase from ~75 to ~125-175. I don’t count calories nor track grams of protein and carbs, but generally I estimate that I would increase consumption ~25-50% on these days as compared to non-intensity days.
For me, hard days leading to a 1.5x to 2x protein consumption would need to be outdoor rides where typical TSS ranges from 225 to 450. (50-100mi w/5k-10kft). If your training base is less, you could scale my #s back to estimate the additional protein you would consume based on a similar approach (i.e. what you are really comparing is how much additional stress you are putting on your muscles vs your normal training load to determine how much additional protein (and carbs) you would need.
Threshold and VO2 Max workouts wouldn’t change the approach. The key thing to recognize, though, is that the higher the intensity, the less the total TSS you will accumulate to get similar stress on your body (i.e. not all TSS are created equal). Perhaps a way of thinking about this is that 100 TSS of sweet spot might be the equivalent of 80-90 TSS of Threshold and 70-80 TSS of VO2Max.
Your body can store glycogen for approximately 60 minutes worth of hard intensity or 90 minutes of endurance. So If you have eaten a meal of sufficient protein and carbs 1-2 hours prior, water should be sufficient. But you could supplement these rides with energy gels/shots and electrolytes as needed (as I do). If you haven’t eaten, what I do is use powders that can be absorbed quickly (I use Hammer Nutrition’s Heed and Sustained Energy). I also supplement as above.
For longer rides, I use Hammer’s Perpetuem. Sometimes I will eat an energy bar, but these are converted into energy more slowly than powders so they should be consumed earlier in the workout.
I hope this helps.