1) Does fast give any bonus when disembarking a transport or you still limited to 6" maximum move after disembarking? It's not mentioned in the rules so we assumed Fast units were still limited to 6" after disembarking.
2) Can units disembark a transport when on their activation after the transport they are in rushed or charged? Again it's not mentioned so we assumed it's fine.
3) Are there any limits to what a unit can do when embarked in a Transport vehicle if they choose not to disembark? Can they shoot out of a transport? Can a Psychic cast a spell?
2) Yes they can disembark on their own activations after the transport rushed or charged.
3) They can do anything they want, but they can do nothing that requires LoS outside of the transport, since other units block LoS, but they can use LoS based abilities like casting on targets inside the same transport.
Ah... Pays to read carefully. We have been charging out of transports like the vehicle was part of the same unit. That is sure going to tone down the orcs and trucks. I see some ranged upgrades in their future!