Popping in here rather late as I have spent a lot of time reviewing lots of running advice on Dis and have some questions specific to this thread. Thanks for your patience and your time should you have some to spare!
More than happy to help! These are great questions and show you're really thinking hard about this.
The line of thinking that brought me to these questions is considering what kind of training plan is appropriate for a person with little range in pace. I can do all the calcs from your quintessential running post, but my pace is what it is and that is slow and not that variable if I want to maintain it for >30 seconds, so line me up early based on VO2 max and then just put me at the end of the line! While Galloway is totally time based, I'm not in love with his plan structure for reasons I cannot articulate, but I do see the appeal and legitimacy of lower total daily miles with cumulative fatigue.
The question is, how do you know you have a little range in pace? From my own personal experience and the experience I've gained working with others, this statement seems true on the surface for most of us. Most in fact struggle to slow down to the paces that I prescribe because in some cases it feels too slow or unnatural. It's definitely an individualistic process though as I've made modifications after a few weeks when some are unable to slow as much as I'm looking for.
When using run/walk, the first place I'd look to is the pace at which you run and the duration of the run/walk intervals. That tends to be where we can manipulate things in order to aid in slowing down or speeding up. So I'd say don't give up quite just yet on pace variation. If you tell me a recent 5k/10k time, then I can go from there in designing run/walk intervals. From there we can see what type of variation we can get.
Early on in this post, you discuss running a total time at a pace vs. running a distance at a pace. Your posts here and elsewhere indicate that you are more focused on cumulative time than distance.
This is true. In my view, the mileage is mostly irrelevant. It's merely a function of what I find to be the more important aspects of a training plan.
1) The relative current fitness pacing.
2) The duration at which you run said relative current fitness pacing.
It's my belief that effort defines the run. There are surrogate measures we can use to evaluate effort such as breathing, pace, and HR. I believe that choosing an appropriate pace structure is one of the single most important aspects of a training plan because of the myriad of benefits of the different paces across the spectrum. But choosing an incorrect pacing structure can lead to issues such as "Surviving the training, instead of thriving because of it."
I use the following chart as an example:
Not the easiest to read, I know, because of it's small size. The pacing structure shown here goes from the easiest of pacing that requires little to no effort, to the fastest end of the spectrum (such as mile pace). You can certainly run faster than mile pace, but for the purposes of recreational endurance runners it doesn't serve a great benefit. Now the important part is choosing the pacing spectrum. If you choose based on "current fitness" you're choosing based on current relevant physiological responses in your body. How your body reacts to a nice and slow pace vs a Lactate Threshold pace vs a VO2max pace varies wildly. What I try and illustrate in this is that the pacing spectrum for easy/long is quite wide. But as the pace quickens, the window for that pace shrinks. So if you choose a pacing structure that's too fast, you could suddenly be doing a "5k" workout using "mile" physiological responses. You're likely to end up with a "Survive the training, instead of thrive because of it" situation. You'll either end up too tired to finish, too tired to do another workout the next day, or end up injured. The stimulus/adaptation/recovery response is the basis for the entire training model. Disrupt that and cause too much focus on the need for repair (because pushed too hard) and you'll find yourself with little time to adapt (and thus a stagnation of improvement).
Now on top of those paces themselves, is the amount of time spent at that relative fitness pace. I believe that each of these physiologically relevant paces have a window of duration that helps aid in that stimulus/adaptation/recovery response cycle. Too little time and you don't get the realized gains. Too much time and you disrupt the cycle and force stagnation. So my focus is on the duration of particular paces that are relevant to the user based on their personal history for each individual workout. The mileage that comes from that is simply a by-product. I could write the plans as more time based, but people don't like that. We as runners tend to like seeing a mileage based plan. So I write the plan based on time, and then give it to the person based on mileage. All along they're following a time based plan though.
(1)when you write your plan you are really calculating total time/week as opposed to the written distance/week?
Neither really, but #2 will explain it.
(2) Is this time [or I suppose distance if the previous answer is no] uniform for all the plans you create or do you vary it?
No. The plans are based on question #8:
8) How many and which days are you willing to run each week? How much time on those specific days are you willing to devote to running? (Most important question, so the more detailed response the better.)
When I write a training plan, I have one big goal (and several smaller ones). The big goal is to write something that the user can follow 100%. It won't be followed 100%, but as close as the user can get is ideal. So rather than write a plan that the user has to work their life around. I write a plan that works around their life. The user tells me how many days per week and how much time on those days. So that means the custom plan can be 3, 4, 5, or 6 days. The time per day could be limited to 30 min or 180 min. Or it could be no running on Tues/Wed/Sun for some variety of reasons. Every individual is different in their response to this question and that's where the game begins for me. Fit what I want to see the person do over the time period given to me (both from a weeks till race day and from a time per day allowed standpoint).
Now with that said, I believe honesty is the best policy. So if someone comes to me and says I currently run a 2 hour 10k, I want to train 2 days per week, am limited to 30 min per day, and I want to run a 2:30 marathon in 3 weeks (an obviously extreme example), then I'll be honest and say it probably won't happen.
So there's some back and forth to determine what can best be accomplished. If someone is doing a marathon is when I start to push the number of days per week. I like to see 5 days per week (or even a 4/5 alternating plan). I've done 4 days a week marathon plans, and they've been successful, but they do carry a bit more risk to them.
So the short answer is, no they're not the same. A 3 hour marathon plan might be 9-10 hrs per week. A 6 hour marathon plan might be 9-10 hrs per week. A 1 hr 10k plan might be 6 hrs per week. A 35 min 10k might be 6 hrs per week. It's all dependent on the user and how much time they have available.
But while the weekly time is not set in any way, the workouts which make up the week are in a way. As the pace X duration becomes a consideration based on the time available to me.
(3) is this total time [or distance?] independent of the pace a runner can hold?
Yes. Again, it's based on time available and the history of the runner. Someone could tell me they can do 9 hours per week, but have only recently been doing 30 min per week and I'm not going to take them to their max. Instead I'll build up gradually. Depending on the number of weeks available, they may or may not hit their max available time.
But I've had runners run 6 hour marathons and train for 9-10 hrs per week and I've had 3 hour marathoners do the same. Up until this summer, the hardest training plan I've ever written was for a 6 hour marathon runner. If I had translated that same plan based on my philosophies for most other runners (including myself), they would not have been able to do it. It was very very tough. But that runner showed they were capable of handling that training load, successfully completed the plan, and reaped the benefits.
Thoughts?
I'll do what I can... 
