Hey there and welcome to Poscon!
A newbie question (or more like a foolish one) is one that's never asked!
I'm able to answer some of those:
1) You launch the actual pilot client through the Plugin menu within X-Plane so that statement is incorrect.
2) The POSCON Launcher is a different tool. You have to download it through hq.poscon.net -> Bottom left on 'More Menu' -> 'Launcher Download'. That one needs to run - but can be in the background.
3) You need the browser once when you start the Launcher to log in. Then once again to file flight plans and possibly see other traffic/ATC on the live map which you can also do on phone, tablets etc. (if I am not mistaken that is)
4) Not that I know of so far but one of the developers or the big boss himself will have to reply to that.
5) The site works normal on my end
6) From what I know it shouldn't be any issue at all, but same applies as 4)