deepstriking transports

Can the unit disembark from the vehicle on the turn it deepstrikes? and does the unit only snap fire from the transport?

As far as i remember yes they can but no assault and no they fire as normal because the deepstrike counts as moving combat speed.

Im not 100% sure but thats what i remember reading

This was a big change with 7th ed.
DS vehicule now arrives at combat speed (0-6") instead of cruising speed (6-12") as it was in 6th ed.
So yes, passengers can now fire at full BS. That's what makes Raider w/ splinter rack better than before... and "yes" Medusa can use their template from an open top vehicule

You can disembark, but you cannot assault, because passengers are arriving from reserve this turn.