I know very little about olives/oil, but the little bit I do know:
One way of starting to identify the different trees is one type has a straight trunk, the other has a twisted trunk - the ones with twisted trunks started to go black earlier than the straight trunk type - at least this year.

Talking to the man in the mill, the oil is of lower acidity and higher quality if you have green olives than if they are black - black ones have more water in them, so if you're after your own oil take them when they're green.

I often wondered what the ratio was in terms of Kg of olives to litres of oil - it varies greatly and even the mill people don't know until it's done - for example, we took in 140Kg of olives and the chap at the mill said we should expect 20 - 25 litres of oil from them - we actually got 46 which was a suprise to both him and us - and the acidity was 0.4% which is extremely good!

As to identifying trees, good luck!  There are big olives, small olives and medium sized ones :)

Nigel