[Maybe]

I did pretty much the same thing you're doing, starting from basically the same level running-wise. I was in pretty decent shape from biking, but due to a nasty crash I had to stay off the bike for a while from physical and mental reasons. After a 5k last Thanksgiving that ended in a bar, I made a 10:30 in the morning drunken decision to run a marathon in a respectable time.

First thing, unless it's hell weather wise, get off the treadmill. If gaging your distance is the reason, then worry more about the time spent out. Early on, that's probably even more important then distance, you just really need to build a solid base.

Building that base is the most mentally and physically challenging part, or at least it was for me. I don't remember where exactly it happened, but runs turned from draining, hard to start/finish-work to enjoyment and relaxation. As long as you don't over-train yourself into an injury (don't be afraid to take days off if something hurts, you won't lose anything), you'll hit that point as well.

Also, don't worry about listening to music. There's a good chance your marathon won't let you use headphones (some are more lenient then others), so when you get close, it's worth getting in a few long runs without music for mental reasons. But until then, you'll be spending a LOT of time on the road, it can get awfully quiet out there without something.