I started running this year, and it took me a while to understand and actually run at slower paces than I was expecting in training. I can understand where you are coming from - you want to work to a particular target and shape your training around this.
At the moment it is the time for base building - slowly clocking up the miles, and by December / January you should be running close to the base mileage expected of the plan you go with, and capable or running the longest session that you have in the first week or two of the plan.
If you really want a target time now, then I don't put much faith in 5k times. You have a 1:44 Half with little training. This would suggest a a marathon time in the 3:40 region with training for the marathon. But, I would expect you to improve on this half marathon time with consistent training. Maybe start off with 3:30 so that you have some training paces. For my first marathon I started off training at sub 3:30. Following a couple of half marathons and good progress in training, I changed to sub 3:15 which was achieved comfortably. As an alternative, training to Heart Rate removes any pacing questions - you run to set heart rate zones for different types of run. Personally I prefer pacing.
Like me you are a relatively new runner and will probably be weak on endurance. Most Marathon plans will have plenty of sessions that are long and slow. For now as has been suggested, it is all about base building. Its a long way to VLM - slow and steady, and the odd tempo run will put you in good stead.
Edited: 15/11/2012 at 22:58