So I just read through the Galloway 10k plan on runDisney and can definitely see why it is confusing. So in general to determine optimal training paces you use something called a "race equivalency" calculation. It's a calculation that says "if you can run distance1 in X time, then you can distance2 in Z time." So for your purpose you can use either your:
1) 5k result that's upcoming
2) Magic Mile (where you run a mile at about 95% full effort) after a warmup and cool down
3) The 800T as described in the instructions found on the plan. The 800T involved running at a pace where there is calm breathing and no huffing and puffing for 800m (roughly 1/2 mile). Then doubling that time + either 3 min with no huff/puff or 4 min with huff/puff. This will give you your weekend long run average pace.
If you use the 5k or MM result, then punch the value into a race equivalency calculator (like the one on Galloway's website here:
http://www.jeffgalloway.com/training/magic-mile/) and it will convert to tell you your goal weekend long run average pace. It will take a bit of back calculating to use the 5k result.
Alternatively, you can just tell me the value for 1, 2, or 3 and I can do the math for you.
Once you have your goal weekend long run pace (which is usually 2 min/mile slower than M Tempo), then it's necessary to hone in on the run/walk intervals. In general, Galloway recommends a 30 second walk interval for most all fitness levels. I go a little more in-depth here talking about the thought process behind the 30 second walking interval.
Some science for run/walk methodology
Boiled down, I believe Galloway has found that the 30 second walk break works optimally because it forces the runner to slow down the run portion of their run/walk. By slowing down the run pace, it better manages keeping fatigue at bay. On the Galloway calc page you can see some suggested starting points for run/walk intervals based on what your weekend long run pace is. It's important to note that this easy/long run pace (weekend pace) should feel very easy. It's not a matter of whether you can go faster than this, you certainly can. But the key to endurance training is "Train slow to race fast". It's completely counterintuitive, but there's lots of science behind why the methodology works. Alternatively, if you do a "PR the day" type pacing you'll find some gains, but you'll stunt your overall improvement.
I've personally developed another calculator that supplements the Galloway equation. Going one step further and attempting to optimize run/walk pacing for each individual person. I combine the Galloway method with the Jack Daniels' teachings on physiological responses to running. Here's an example:
Let's assume the 13:50 min/mile pace you recently did on your 2.9 mile run was indeed close to a 5k PR pace. Not saying it is, but for the sake of example. With good training this is what that same person would be capable of at different distances (race equivalency calculation):
View attachment 480023
Then, these race paces suggest the following training paces:
View attachment 480024
The key to determining the run/walk pacing for this calculator is determining your walking pace. So I typically suggest people just go and comfortably walk outside for 0.5-1 miles. Practically no effort and not a brisk walk. I use that value as the walk pace. Then the calculator spits out suggested run/walk ratios and goal run paces. So for this person above, their suggested Easy/LR pace is a 17:44 min/mile average. It's based on a 15:44 min/mile marathon tempo + 2 minutes. So this person would do a 30/30 at 17:09 min/mile run pace and 18:20 min/mile walk pace. It then has different suggestions of run/walk pacing and ratios for other racing distances or training paces.
Hope that helps and let me know if you've got more questions. I know this is fairly dense, so I can explain anything more.