I know the schools have a good reputation, but can't tell you much about them. I know that people want to move to our catchment area in order to get into Courtlands, so you could do some checking on that one, Mill Hill County is another, and there is a Jewish school near the top of Mill Hill Broadway (used to be a garden centre). Google will give you the names of the others.
Parts of Mill Hill cheaper than others and Mill Hill East is getting a facelift, used to be Army Barracks there and now lots of new homes, and Waitrose is that side.
Mill Hill quite big, so there is a vast choice of prices, it is not as packed in as Muswell Hill, which is more trendy and hipstery, and I think overpriced, probably due to Alexander Palace being there. We looked at it and rejected it on the grounds that a small terraced house cost waaay too much. It is also a bit further from Central London.
If you need a mainline station it is by The Broadway, underground is Mill Hill East, plenty of buses. Lots of places to eat in The Broadway too.