Don't be an idiot.
They are taking up way too much room.
Nah. Any ones you need to keep will be locked into the 'Quest Items' tab, and once you've read them they'll be sellable. One thing to keep in mind is that with the gear maps, if you sell them and rebuy them, at the minute they seem to get stuck in your Quest Items tab forever. Not really a big deal though.
Not that I know of, but you should always read them first to make sure they start the quests before selling.