Z21 and Detectors - Question

[Herri]

I am planning a layout in HO, having been away from the hobby for many years. Looking through many hours of Youtube and various forums,I have decided on the Z21 and iTrack.
I am expecting around 16 blocks and the same on points.
However I do not understand the difference between the 10808 detector and the 10819. Both say they are for block detection and cost the same. The 10819 will detect 16 blocks but the 10808 only 8.
1. Can someone explain please?
2. If I want to stop a train at a particular stop, (second occupancy sensor), does this occupy a second slot on my detector?

Many thanks
David

[RFS]

The software you mention is iTrain rather than iTrack, and I would suggest you would be best joining the iTrain forum and asking this type of question there where there are people familiar with these products.

As with Freiwald Traincontroller, which I use, you can configure automation with only a single occupancy detector per block.