I love grinding so that's no issue, iv'e been reading around and its a 50/50 between skip the first four and jump into GU and others say play them. So I'm going to buy the first .hack as well as GU and just play both.
But also .hack is spread across so many different mediums when it comes to its story, where do I begin ._.
I love the entire series but if you don't want to play the first tetralogy you can skip it, especially since the games are pretty expensive used.
G.U. trilogy is a fine place to start and honestly you'll just miss some references to the past games like a character might be controlled by a player who also had a character in the first series.
If you really want to play/read/watch it and only want the minimum required to get the full experience without any alternate perspective stories or irrelevant side stories, start by watching .hack//SIGN, then read AI Buster 1, then play the first four games while watching the Liminality OVA.
After beating the fourth game, read AI Buster 2 and move on to the manga Legend of the Twilight. Skip the anime for this one as it deviates from the manga's story and is not considered canon.
Now you're in the G.U. era which begins with .hack//Roots. It's not as good as SIGN but has tons of important character development and introductions for the G.U. trilogy.
Now you can play the three G.U. games.
Once finished with those you're in the final era and can import and play Link if you want.
Then you've got .hack//Quantum to watch which can be found free and uploaded by Funimation on Youtube. It also works as a standalone series and at only 3 episodes serves as a good introduction to .hack in itself.
After that you've just got .hack//The Movie and the Thanatos Report to tie things up.
I left out a bunch of light novels and manga adaptations as well some little sequel things but as near as I can tell this should be a decent guide to the order of the .hack series.