All great advice.
In general realize why your training and what the numbers actually mean. 100mpw is an arbitrary number, think about this:
If you trained by time and not mileage (pretty popular method) and you averaged 7:30 miles your 100mpw would be 12:30 minutes. Might as well run 13:00 hours, but then you just ran 104 miles.
If you using the metric system it would be 161, doesn't have the same ring to it huh? Might as well 170, but then you would or ran 105.6 miles
With those fun facts realize what 100mpw does mean. It means your putting in good volume of aerobic running. And a few 90+ mile weeks will always beat someone that runs 70 on average and threw in a 100mpw. (volume wise, he could still kick your a$$ in a race, who knows)
Now think about which system you would stress if you ran 3 miles? What adaptations would come? 21 minutes of running at best?
My advice? if you never ran 100mpw before, put your shoes on and go for it. But after this get it out of your system and realize that chasing arbitrary numbers will get you no where, and may even get you hurt.