I think these questions are answered in the ST forum link I posted. However, this is my understanding:

The training specification is very simple: there are 3 zones. 1 = below VT1, 2 = above VT1 and below VT2, 3= above VT2. All training is to take place in zones 1 and 3. Of course if using a HRM there will be transition HRs in 2 while heading for z3. These count the same as 3. However, you don't really need a HRM. You just have to know where VT1 and VT2 are and what they feel like. This takes a little experience. It doesn't matter the exact HR or intensity you feel, only that you are going as hard as you can for however many minutes. FI in 4 X 4, you go hard enough that you'd blow up if you extended an interval even another minute. The same for 4 X 8: you can't do 10' at that effort level, only 8. This automatically puts your HR or effort in the correct percentage of MHR, FTP, or RPE. Once you've done a few intervals, you'll know what it should feel like. As was said, it's important not to go out too hard and blow too soon, and also that it's important that your first interval be the easiest so you'll know where you are.

What was found to work the best is to do 20% of training sessions in zone 3. So if you trained 10 sessions/week, 2 would be interval sessions; at 5/week, 1 would be intervals. The z3 volume that is recommended for optimal performance is 2 sessions of 4 X 8 per week. To keep the percentage of volume ~10% or less of z3 per week, optimal training time would therefore be 10 hrs or more total. Z1 volume could be then most anything, say from 5 to 20 hrs./week. At the low end, you'd do 1 interval session/week. At the 10 hrs.+ level, you'd do 2 sessions. They were a bit unclear on that detail. There is some suggestion that 2 sessions should be done no matter how many hours of z1 you have. I think one would have to experiment and see what worked best. That's a huge takeaway: each athlete has to develop their exact approach to these things based on their personal experience.

Yes, the entire volume of easy workouts must be below VT1. One should learn to recognize VT1 by oneself. However going by Friel's zone 2 would be a good start. Throwing even a little z2 or z3 into a z1 workout is not recommended. It's a lot less boring inside on rollers. If more than an hour drives you nuts, do two a day.

They found the stimulus of 32 minutes (4 X8) at maximum 8' intensity to create the best response. Longer intervals would necessarily be done at a lower intensity. The whole long-intervals-at-or-below-threshold thing is out the window. In this plan, you don't do them except during competition. The principle of specificity is out the window.

No, what they mean by oxidative flux is the amount of oxygen consumed, nothing to do with intensity. This model works equally well for the trained and untrained: they don't do anything differently. The untrained just process less oxygen for the same RPE and thus go slower. It may be true that the untrained will have less trouble working beyond VT2 than a trained athlete, but I doubt it.