Much of the foundation is, well... foundation. Limited down-time between seasons (If any at all - I consider my down-time to be two weeks of easy running), a reasonable buildup, then week after week of training bordering on OCD. Sometimes for several years before the breakthrough, though if you find the right plan that works for you it could only take a year. If you were a 4:06 guy in college, chances are it's going to take a lot of consistency to drop that much time unless your training back then was sub-par.
I coached myself to a sub 4 but I had been coaching myself for several years and kept making slight tweaks to my plan (which was just bits and pieces picked up here and there) based on what I thought was working for me.
Be careful listening to anyone who has a 'plan'. There are plans that are generally better than others, but nothing is going to be the best route to take for every runner. In your situation, you're going to have to really get a feel for what's helping you and what you can do without - and do this as quickly as possible. My 400, 5k, and 8k aren't drastically different than yours (a bit slower at 400, moderately faster at 5k and 8k) so you can take this with a grain of salt, but here's what I found to work for me:
For aerobic development
-Decent mileage. 80-85. Comfortable.
-Good long run. 18 miles Comfortable.
-A lot of tempo. Twice a week in base phase alternating between straight tempo (8k, 10k, or 12k) and long tempo intervals (6x2k, 4x3k, 3x4k w/20% time rest). Gradually cutting the pace over time. I was able to comfortably hit anywhere from 4:55 - 5:05 pace depending on the workout by the middle of race phase. These workouts were less frequent and less voluminous as the season moved on.
For speed
-Strides a few times a week.
-A lot of work at (what I estimated to be) current mile pace. Once a week during base I'd do about 4km worth of 200s and/or 300s. 20x200 with either 100m rest in :45 or 200m rest in 1:00 was a staple. I'd change it up for variety, but the intervals and rest were always short. 12x300, 4x(2,3,3,2), etc. Nearing the end of the season, I'd try to do longer intervals for these workouts - 300m, 400m, and 500m reps.
-Every few weeks I'd try to get some pure sprinting in. 100m or 200m reps with full rest. I think more of this would have helped me, but I was squeezing a lot of work into very little time and these workouts didn't make the cut since they made it difficult to get my mileage for the day and I felt I got more from high-volume workouts.
I almost completely cut out mid-length intervals at 3-5k pace. They became too much of a hassle since I greatly struggled to do them by myself and most of the time I felt I wasted a day of training trying them. Certainly never ran them during base. Once I was near race phase though, I would throw in 20x400 w/100m rest at about 3-5k pace which I could manage alone. Only 2 or 3 sessions of 6x1k or similar and I had to get into a zone to do them (probably why my 5k PR sucks).
Good luck. If you're interested in more from me specifically just ask - I'll keep an eye on the thread for a day or so. I've got a training log you could look at.