runwiththewind: Everyone is different and will take a route that suits them. For me what worked (when increasing distances from HM for the first time) was training from October HM towards a 50K in January (increasing distance and starting back-to-back long runs) then training for a marathon in April (reducing distance on the long runs but increasing speed work compared to training for the 50K), then increasing distance and back-to-backs again for a 50-miler in August. Training schedules available online can be useful to give you an indication of the sort of mileage you might want to aim for.
Saz: a friend of mine had a severe bout of pneumonia requiring hospitalization several years ago. Not a runner, but I remember she said it took a long time before she was back to normal - two years, not six months, although with a lot of recovery in the first year.
If you're having problems breathing then I suggest you repeat a week on the C25K programme, even drop back and repeat the previous week, and see how that feels. Once your lungs are feeling like they can cope with a bit more, try stepping it up a bit.
I -do- know how frustrating it can be, as I'm presently trying to get my mileage back up after a tendon tear (cycling accident!) had me off running for six months: I was running 50-milers, with 20-25 mile LSRs as standard, and now, six months after I restarted, my longest run has been a whole 12 miles. I tried to increase mileage sooner and kept having to step back.
So take it gently, run slowly, allow your lungs to repair. And good luck!
It really is try them and see. I've used twin-skin socks on all my marathons and ultras (up to 50 milers) so far and they seem to have worked (no blisters). Presently using Karrimor ones which have some padding, are L/R specific, inexpensive - and come in mostly black and grey which is sensible for trails! I'm going to see how these do as I increase the length of my long runs again; so far they've been fine for up to 12 miles.
RebeccaV: REST. Go t your GP. Get a diagnosis if you possibly can. The other thing to consider is that if it's not a stress fracture then you've got a possibly-serious soft tissue injury - which may, unfortunately, take longer to heal than a stress fracture would take (I speak from the experience of having had a metatarsal stress fracture stress fracture (six weeks off), extensor tendonitis (three months off) and posterior tibial tendon tear (six months off and very gradual return to running).