As far as I know, Sandringham has quite an Indian community and so does Flat Bush and Mangere. All three are very different.
If you're considering from the point of view of Indian groceries availability, check online for their presence. If you're thinking adherence, it may be a bit difficult to pinpoint and you may later be disappointed with your expectations.
Let me tell you my personal experience. I'm Chinese from Southeast Asia. Before moving to Auckland, I so wanted to live in Pakuranga/East Tamaki area for probably the same reasons as you. But we settled in another neighbourhood elsewhere in South Auckland. From time to time, we still go to Pakuranga for Chinese restaurants, groceries and 'friends'. Over time, we've established that we'll not live there because we hated the traffic and the way those crazy drivers there drive. And oh the snobs. Our two groups of 'friends' also became snobs because they thought they've done so well living in a good neighbourhood. Truth is, they're having a really hard time with the expensive mortgages and husband-wife can't afford to lose their jobs.
I know this is probably an extreme example. What I'm saying is, don't be too fixed with a certain neighbourhood or with expectations of your life there. Find a house that is warm and on a good street. Drive by during the day and night, check rush hour traffic, search for nearby amenities, etc.
Auckland is only a fraction of what Melbourne can give you. If you're already very settled and happy in Melb, do consider to stay there.