@aglrocher first of all I think your game plan sounds solid! 
When I say VO2 I mean really the amount of oxygen being consumed at any point in time. VT1 is easy to find (for me, anyhow) if you know your respiration rate and the amount of oxygen you are consuming during an incremental ramp test. You just watch the ratio of those two over time…it stays constant until you reach VT1 then the ratio will ramp up.
In other words, after VT1 respiration rate starts to increase much more than oxygen consumption. It’s super, super obvious when you look at the data! Not like VT2 where three people can look at the same data and come up with a little different number.
But you don’t need to know exactly what your VT1 is…you just need to know that you’re comfortably UNDER it. For me VT1 happens at or around 75% of peak HR pretty consistently so if I cap heart rate at 65% I always feel like for sure that’s under VT1. If you use that target and make sure you’re conforming to the talk test you’ll be good!
GOOD LUCK ON YOUR RIDE! Sounds like it’s gonna be awesome.