Yes all hangers at an airfield will take 3k of bombs to kill.The excecption to this is that Vehicle hangers at V fields & ports can be killed with a single 1k bomb.
(Tip, try dropping a 4k bomb from Lanc square between 2 close fighter hangers)
As long as one hanger type remains up all planes will be able to take off. Example, medium fields have only 1 Fighter hanger. Kill it and they are unable to roll fighters.
There is no effect for killing some of a hanger type. It's kill them all or nothing.