I see. Makes sense. In that case, I would personally treat both of them as goal half marathons. I wouldn't even call the first one "training". I'd approach it as the goal, and then have the other as a backup or goal #2 IF you recover well from the first one. Otherwise, racing a half marathon 1 month prior to your goal half marathon is probably not ideal, and could be risky. Some will handle it ok, and others won't. I would guess your lower weekly mileage would increase your risk in that case. Part of the problem is that you have to recover from race #1 (1-2 weeks for a half?) and yet you're still 4 weeks out from race #2 which is too early to taper. Racing a 5k or 10k a month out from a goal half is probably more ideal.
My pleasure. Hopefully some of it helps you avoid learning via the school of hard knocks. (which is where I learned many of them).
That sounds good. Anywhere between 3k-5k pace seems to work well for most people for these VO2max intervals. And, should be a good training stimulus for both the 5k and your half marathon(s). I would just go for a solid effort around that ~5sec/mi slower than 3k pace, and not get too fixated on a particular pace each workout... one week might be a few seconds or even several seconds per mile slower for whatever reason. No big deal. Just know that you can get a nice training stimulus with anything between 3k-5k race pace, and that will help you relax.
As for the rest, 2:00 is good for your 800s. I'd say for these VO2 intervals, three minute workbouts, get 2-3 minutes jog recovery. Four minute workbouts take around 3 minutes. Five minute workbouts you can take 3-5 minutes jogging and still get great results. I wouldn't go much over 5 minutes per interval for VO2max pace... so maybe keep your longest ones 1200m until you get faster. When you start going beyond five minutes it makes it very difficult to hit the proper effort level for the full workout.
I understand your thought process.
Where you're going wrong is that you need to understand the purpose of each type of workout. Your VO2max workouts are not really to prepare you for the length of your half marathon. Your long runs & overall weekly mileage will do that.
The VO2max intervals are to stress your aerobic capacity, or VO2max. They will also get your body mechanically used to running faster than race pace (both 5k and HM race pace) which should make those paces feel more comfortable mechanically.
Your half marathon pace training, in the form of continuous runs & long intervals will improve your economy at HM pace, mentally callous you to the effort at that pace, improve your lactate threshold, etc...
The problem most of us run into by attempting the bigger (too big?) workouts is that you suffer in other areas of your training such as 1) overall mileage; 2) frequency of quality workouts; 3) recovery to improve from your training and avoid getting in a hole.
It is the combination of all those factors that will give you the best preparation for your half marathon. Do too much in one area, and you can't optimally hit all the others.
For your 50 mpw, I would only do 5 x mile if it was at threshold-to-half marathon pace. I definitely wouldn't do that much volume for faster VO2max intervals. Honestly, three miles at VO2max is plenty. I would definitely not go above 8% of weekly mileage. As an example, I was able to drop my 5k time (all in my mid-30s) from 21:00 to 15:45 and never did more than 5k (3.1 miles) in a single VO2max workout. It was only now, running 70-80 miles per week, that I've starting introducing 4 miles of VO2max intervals (~5-6% of my weekly mileage, so well under that 8% limit).
If you want to understand more about what each piece of the training puzzle is supposed to accomplish I recommend reading the book Daniels Running Formula. It will give you a nice knowledge foundation.
I think you are on the right track! Good luck and train hard (but smart!).