Andrew,
An example training plan based on what I've used for training for long distance events
Training Plan
Easy to vary the length of the long run progression if you want to max out at shorter long runs, the danger of running too long is increased injury risk but the benefits are you're more prepared for the distance. All other runs have warm up and cool down in additions to the session. This is a 3 run a week plan, you can run more by adding recovery/steady runs or by knocking out a tempo run and putting something else instead.
Key points in any plan, is to make it progressive with recovery phases built in.
There's all sorts of different approaches though.