Hi and
so to your questions.
1: Displayport is a Digital Signal type, so you won't have any quality loss if you have a cheap cable. For the input lag, the transcoding is done nearly instant. So you won't notice it.
2: uhm.... well, there is also a little problem with Displayport. You never know whats happening, in my case i never had these Problems!
3: obsolete. don't spent 100$ for a dual link if you don't need 120hz !
4: AMD has this official List.
http://support.amd.com/en-us/recommende ... y-adapters though, thats kinda short, i'm sure lot's of other adapters will work fine too.
5: ah well, no. The chance that a "high quality" brand will mess up/use cheaper parts is smaller, but how can you be sure they're really high quality and not not just marked high quality ?