How to start the .hack series and its viewing order? As the questions suggest: how do I start and what is the preferred order?

It would be appreciated if one would also identify which anime/film/OVA has a main story. Additionally the timeline of which anime goes where would be appreciated as well.
The release order of .hack is:


.hack//Sign 
.hack//Liminality [OVA]
.hack//Legend of Twilight (Tasogare no Udewa Densetsu)
.hack//Gift [OVA]
.hack//Roots 
.hack//G.U. Trilogy [Movie]
.hack//G.U. Returner [OVA]
.hack//Quantum [OVA]
.hack//Sekai no Mukou ni [Movie]




If you want to watch each story at a time, I would suggest:


.hack//Sign 
.hack//Liminality


Because they share the same storyline. Then,


.hack//Legend of Twilight
.hack//Gift


As Gift is a side story to the other three you have now watched.

At this stage there are two distinct storylines you can pick from:

1:


.hack//Roots
.hack//G.U. Trilogy [Movie]
.hack//G.U. Returner [OVA]


2:


.hack//Quantum
.hack//Sekai no Mukou ni [Movie]


Finally, pick the story you didn't choose to watch in the last choice



Here's a flowchart from AniDB: