Hi
I grew up on the Central Coast, so I know it fairly well.
Niagara Park, Narara and Lisarow are all on the train line between Newcastle and Sydney. They aren't very close to the beach, but the good news is that you can easily drive to many beaches from there. You can drive out to the peninsula to Ocean Beach at Umina, or drive to Terrigal in about 15-20 minutes. All are family type areas. Gosford close by has been in a decline since Erina Fair (the massive shopping centre at Erina) was built in the late 1980s. The local government have tried and tried to regenerate Gosford, but to no avail as yet. That has given that end of town a bit of a bad rep in some ways, but Lisarow, Niagara Park and Ourimbah are all fine.
Wyoming has a reputation for being a bit rough. I lived there for a year in 1998, and had no trouble at all. If you are planning to commute to Sydney for work, you could also look at Tuggerah, Woy Woy, Umina, Berkeley Vale and Killarney Vale - these are all easy access to train stations. One thing to be aware of is that the trains that stop at the minor stations (Ourimbah to Narara) are all the slow trains. The fast trains will stop Tuggerah - Gosford - Woy Woy etc. Berkeley Vale and Killarney Vale are towards the northern end of the Central Coast, but are decent places to live. Bateau Bay still has some affordable properties - but on the west side, all the ones near the beach have been snapped up.
If you have any more questions, feel free to PM me, I'm happy to answer any questions you have.
Good luck