Okay. First, what was the nature of your "fracture"--an accident, or (more likely) a stress injury? If the latter, what will you be doing differently (this summer, yes, but also long-term) to prevent its recurrence? Just hoping, or something more proactive, like strengthening or form correction or different shoes, etc.? What level of mileage AND overall stress (e.g. shortened or irregular sleep, academic/relationship/personal stress, other health problems, etc.) were you facing when you got hurt? A big boost in mileage, with no other changes in routine, would simply make you likely to get injured again. In particular, work on core: the front page has a link to a good program--scroll down to find it--and Pete Pfitzinger's site also has some good info. An overall strength routine, *including legs*, is also a good idea. Check with your coach or school trainer for a good routine; 45-60mins. a week of strength work can pay huge dividends in performance and injury prevention.
Second, a lot of people (though not all) have encountered difficulty when they've done nothing but running for extended periods. Consider working part-time (the added income will mean less pressure to work, during the coming school year), or perhaps taking a summer course or two...*something* to give structure to your day, and to keep you from thinking only about your next training session.
Third, I applaud your idea of starting doubles. It's a great way to add mileage while adding little stress. However, don't just jump into it; start with maybe 2-3 mornings per week, then add another morning every fortnight or so. This gives a nice, "free" (because you'll recover from it so readily), incremental boost to your weekly mileage as you progress through the summer.
Fourth, it's great that you're thinking long-term about the doubles and looking at keeping them during the school year. Realistically, when would you be doing them during school--6am, 8am, 9:30? You can do them whenever you want to now, but as the summer progresses you should gradually move them to match the time that you'll be doing them during the school year. Similarly, naps now are fine--take a 20-30min (not longer) nap whenever you feel the need--but if (frequent) naps are not realistically possible once school resumes, then you should gradually wean yourself from them over the last weeks of summer, understanding that you'll need to make up the recovery somehow, maybe through more sleep at night.
Fifth, you should similarly take a realistic look at what your *sustainable* sleep schedule will be when you start classes again in the fall. You'll want to follow that schedule every day (yes, weekends included) then; and, once again, you'll want to move toward that schedule as the summer progresses. As part of that, get in the habit of counting your pulse for a full minute in the morning, before getting out of bed. Pulse is a convenient guide to how you're recovering: if it's above your normal, especially by 10% or more, then you haven't recovered from the previous day(s) and you need to take today easy, or off.
Finally, stay "in touch" with your speed throughout this off-season period. Nothing generating a lot of lactate, but occasionally get your legs turning over quickly. I understand that Jack Daniels's book discusses this, as have other threads.
Good luck. Have fun. I envy you.