Many of us use ExpertFlyer to track fares like this, others use Google fares or ITA Matrix, and there is a lot more information about this in the main BA Forum Dashboard thread on Finding a good BA fare.

Yes, J to I are CE, the rest are ET, with G the cheapest, the latter usually being the basis of BA Holiday package fares. At the moment it is saying D8 meaning they will sell 8 seats at this price. But once they've sold those 8 D seats, they may change it - in almost any direction.