My general advice:
Long run 15-20% of weekly mileage. If you're running relatively low mileage, lean towards 20%, if you're running relatively high mileage lean towards 15%.
Maintaining 70 mpw is a good goal, as long as you've successfully MAINTAINED 60 mpw of more in a previous year. There's no reason for any high schooler to go higher than 85 mpw and those are guys who, no offense, have more solid training bases than a 16:30 guy would. If you feel good after a few weeks of 70, take a down week and try 75 but I wouldn't hold it for more than one or two weeks.
Tempo runs/fartleks are key for maximizing your aerobic development without terribly taxing the body. Since this will likely be a challenging amount of volume for you, you want to play it cautious with the intensity.
At least every other week I'd do something faster, like 400's at 2mile pace, just because if you rely on strides as your only means of maintaining your ability to run fast you will feel very flat when you do try to run fast in a race or time trial, and racing at a speed your body is not prepared for is a good way to get injured. Just make sure the day before isn't terribly long and the next morning you do an EASY (at least 30s/mile slower than your normal run pace) shakeout. If you feel good you can come back with a normal run in the afternoon, if you still feel sore from the workout do another easy run or take the day off (it won't kill you so long as you accept a slightly lower mileage total for the week)