some quick questions about Co-op

I haven't tried any online stuff yet but I have a friend that just started playing. I know that it is possible to join each others games granted certain parameters are met. Correct me if I'm wrong please.
- I need the soapstone and can be hollowed or not.
-he needs to be human
-within 10 sl points +15% of eachother
-we have to be in an area where the area boss has not been defeated in his game. ex-So no firelink but undeadburg would be ok as long as the Taurus Demon is alive.
-we coordinate an out of the way spot and I cycle my summon spot until he sees it in his game.
-If we kill the boss I get sent back.
Is this about right? Also if i'm summoned in undeadburg can we go anywhere or do we have to stay in that area?

Well, when you are summoned, or when you summon someone, or when you are inavded, white fog walls appear, similar to those that you can pass through, but this ones are locked until you beat the boss or until you slain the invader, so you're locked in the area

You only need the soapstone if you are trying to go into someone elses world, you can host regardless. i thought it was 10% but it could have changed. You have to stay in the area because dark souls is made into sections, and you cant enter certain areas while he is there or an invader.

You've practically nailed all of it. Personally I recycle my sign when I host but I think it's perference should work either way. You can go through the roughly the whole section, some areas that are safe spots may be cut off, not sure on that.

Thanks I wasn't sure about the fog gates.

Also the wiki has been updated to +15% after 1.05 it seems.

yes, you can actually see much more signs than before patch, and much more invasions too lol

So the area until undead parish would be off limits and i could be summoned again in undead parish?

Do both partys get souls from the enemies or do you get only the souls that you kill with your character?

Everyone gains souls, however, phantoms only get half of the souls a mob drops. So if you kill a Silver knight, the host gains 1000 souls, the phantoms gain 500, no matter who landed the killing blow

Awesome I think all my questions are answered now. Once again you guys are great.