Couple of thoughts.
Plug 1:25 into a calculator and you get 18:20ish 5k pace. 1:22 is 17:40ish. Now, you might be 20 lbs more than when you ran low 16's for 5k, but I don't think you're crazy for shooting for that HM range.
If you have time, I would suggest listening to a podcast with a guy I've coached named Mark Hansen. 1:29 five years ago to 1:22 a few weeks ago. He is a busy adult - young kids and a demanding job - and is able to do HM training that has the same structure as the marathon training. I know you're super busy but listening to the podcast will sheed a lot of light on the training. Mark was a 4:20ish HS runner, didn't run in college, then got back into it. I think he's 37-38 years old. Great guy...who had reservations about some aspects of the training, until he ran a nice PR.
Podcast:
https://itunes.apple.com/us/podcast/run-faster-podcast/id969509765?mt=2
The subtitle to the book is key - and therefore is not intended for the message board folk who want to do the training from the Advanced Marathoning book.
"The Right Training for Busy Adults with Hectic Lives."
This sounds like you, and thus the following may be right for you.
The book has you:
Running 5 days a week
Cross training one day a week
Doing a (gasp!) brisk walk the day after the long run.
Lunge Matrix and Leg Swings before each run - 5 min
Core Strength, Hip Strength and Hip Mobility - SAM - after the run - 10-15 min
The focus of each week for the marathon book is the same as it is for Mark: the long run. The second most important day is workout where you run by feel.
Most people run the workout on Tuesday and the long run on Saturday. Knock out the long run Sat morning then you have the rest of the weekend to do as you please. Tuesday is assigned by minutes, so you know how much time you need to get in the work (though in the last 3-4 weeks of the training you need to run an assignment via miles, yet at your HM pace, this would only mean another 10-15 minutes)
If you don't listen to podcasts, email me and I can put you in touch with Mark.
I'll be writing a half marathon book that will be out this spring. The structure of the training is similar, with the key differences being that the training is shorter than the 20-week marathon training, plus the obvious difference that you have enough stored glycogen to run a half, but not enough to run a full marathon.
Bottom line is I want to help.