1) Different farseers will view and pursue different futures and to farseers could come to blows if their visions are conflicting. It's highly unlikely that visions of powerful farseers would diverge on paths dire enough for two craftworlds to go to open war but since they are Eldar you can only imagine the pomp and politics.
1) Some daemon princes of Slaanesh are older in the physical realm than Slaanesh himself. Remember that in the Immaterium Slaanesh has always existed but there were daemons at work in the Eldar civilisation during the fall and at the time they were entities of Chaos Glory.
2) Daemon Princes require vessels to remain on the material plane for long and they destroy their vessels quickly but there are very rare vessels that are able to retain their human form for long periods of time while possessed
by a prince. These powerful infiltrators will be dangerous for hundreds of years even before the vessel gives way and they take their true form.
1) House Belisarius of the Navis Nobilite made a pact to serve Ulthwe a certain amount of favors
in exchange for help when the house needed to increase it's political sway around the times of the Great Crusade. Illustrates how the Navis Nobilite can use they services to stand head and shoulders above the rest of humanity.
2) Warp navigation charts on paper are given their 3rd and 4th dimensions with multicolored threads and secret symbols that are impossible for a non-navigator to
3) Less of a note than just a recommendation. Very decent depiction of warp travel from the Navigator's eye in this book.