OK, you asked. IMO...

You should be completely resting right now. No running, biking or swimming for at least one month after a heavy racing season (and yours was very long and intense), even up to 2 months. You need that break to let everything build back up after all the trashing. It's OK to do light activity of another type eg hiking, kayaking....

When you seriously start back running (which should be about 6 months out from your first triathlon) you shuld use the first 3 months to build an endurance base as the people you have talked to suggested. Use the build by 10% per week rule, that's 5 min same as what you figured out.

As for running slowly, running too slowly will change your stride and can cause a whole different set of aches and pains. I do not recommend forcing yourself to run that slowly, but you should be running slowly enough to stay in a recovery heart rate zone, that means you should be able to hold a conversation easliy while you're running. If you're serious about next season, I would get a VO2 max test done at the beginning of your training season and use an HR monitor to make sure you're in your target zone.

Hope that helps. It's probably not what you wanted to hear.