There are loads of plans around. Most schedules seem to be over 16 or 18 weeks, although you've got 12 weeks which should be enough for a reasonable effort, especially if you run a bit already. There are some on this site, and on halhigdon.com, and on nyrrc.org, and there are lots of books - Bob Glover's ones are good.
To be honest, they all say pretty much the same thing: your week should include
- one long run (building to 16 - 20 miles)
- one shorter, faster "tempo" run (6 - 8 miles)
- some kind of interval run (hills, fartlek etc.)
- other medium runs, whatever you can fit in.
Plus they give some sensible tips
- alternate hard and easier days
- build up mileage gently - roughly 10% per week
- taper as you approach the marathon
As for times, there's no telling. Some people run 6 times a week and do it in 5 hours, some run twice a week and do it in 3. It depends on what you're like. Your times sound quite quick, so yes, you could potentially get a good time.