Galloway's run/walk training program is designed to help you increase speed over time, but more importantly, endurance. The plan should list a run/walk ratio for the pace you want to achieve - that's how many minutes it takes you to run a mile. If you want to achieve a 12 m/m pace, i.e., run a mile in 12 minutes, then, according to his strategy, you would run 30 seconds, walk 30 seconds. The point of his plan is to finish the race. Upright.
The are other good training plans. I'd Google them. For me, the important thing is a plan you understand and can follow. Make sure it includes a 2 week taper plan before race day - that's reducing the mileage you ran the week of your longest run by almost 80 percent the remaining two weeks prior to race day.
If you are going to run on a treadmill, especially for most of your training, yes, vary the speed AND incline. The theory behind increasing the incline is to mimic the wind resistance you incur running outdoors. If you do register for an on-property race longer than a 5k (those are run around Epcot), while most of the course is flat, there are several on-ramps you'll run up (always the 3rd to the last mile of the race). Running on a treadmill with no incline will not prepare you for running UP the on-ramp to the bridge on Osceola Drive at Mile 10 of the Half.
i don't know what other workouts you do, but strengthening your core is essential to running. Squats, lots of squats.
Good luck!
ps - I really don't like Galloway's recommendation for running form. Everything I've read...and practice...indicates landing midfoot, rather than heal, is much better. And leaning forward from the ankles, not waist, naturally propels you forward as opposed to running perfectly upright. Just my 2 cents.
