The regular runners tend to be found in the Exercise topic
www.mumsnet.com/Talk/exercise
There are a few C25K threads, a main Parkrun thread and quite a few shorter ones, a main running chat thread, and loads of threads about shoes, other kit, and just about every aspect of running you can think of.
A Half in 5 months is ambitious but potentially achievable. Spend the first 9 weeks doing C25K, and at least one other strength/fitness class a week (Pilates or weights are the most frequently mentioned complementary activities, but anything will do).
Whilst still doing C25K, start Parkrunning (doesn't matter if you walk some of it).
Have a lighter week every 4th or 5th week (don't stop running, just reduce for a bit, it's good in the longer term to avoid over-training).
Then you have about 9 weeks to double your 5k to 10k (book a couple of 10k events - roughly where do you live, someone might be able to recommend a friendly one?)
And then same again to double your 10k to a Half, leaving a couple of weeks over to taper (deliberately reduce mileage in 1-3 weeks preceding a big event - sounds counterintuitive, but really does help)
It helps to have good trainers and a good bra right from the start.