1st agree with Efrye, a few ppl try to answer ur Qs.. saying thank you doesnt hurt...
that said: to the best of my knowledge...
1. Leader means everyone can see in it, but they can not touch. Full means they have the power to take and put things. None means no one can see in it or touch it. Use Leader if you want to show stuff but limit who takes it by handing it out yourself.
imho.. you should set it as full for leader and officers (i assume you are greating the company with friends) and members to leader. With this setting all founders would have the same access as you. Once you start promoting members to officers u might have to change some of those settings..
2. auntumrain answer most of this. actions are BOOST for members of the company snd can be activate at rank 5 (i think.. still no there.. almost, slmost!!! :P )..the link below give you what each action do:
http://xivwiki.com/Free_Companies
3. answer by others.. crafting, hunting, leveling classes...
4. as HEC and dawnmorerise said..