People are very friendly here (I have lived in Diamo for 10 years). Don't be put off by comments from people who go to Coles and assume everyone is rude. Diamo is much like a country town, where locals tend to know each other a bit more closely than in the inner city, which could be considered snobby to outsiders. If you are concerned, maybe check out the schools and talk to some of the parents (they wont bite). The train is very close to the estate and there is a bike path you can take as a short cut. The trains are ok in peak times, but very infrequent outside of that. In saying that though, the trains are usually pretty quiet and trouble/crime free. The Chinese noodle shop 'Yings' mentioned above has closed BTW as the lady retired. Diamo overall is a fantastic place to raise a family and has a great balance of quiet, scenery, good coffee (at Piccallo) , bike paths, parks and as mentioned friendly locals. The only angst you may experience is locals peeved about increasing traffic due to the new developments (but the council cops all the blame for this anyway). All the best with your move.
I do not live in Diamond Creek myself but I do frequently go there to see my best friend. I haven't met anyone extremely rude and quite a few people seem nice. There is especially this lovely lady who runs a Chinese shop called Yin's. Personally I hope you get the/got the lot because it is a really nice place.