I am only 25% done at rep, but I have seen a few players flying around already. How far are you at unlocking flying? Is there any trick to speed up the rep farming?

do wq in broken isle daily...Human racial + darkmoon buff...keep farm the war supply by killing rares..i only around 45%...= ="

I think i knew how they did it. i went and finish all available questlines on broken shores at the moment, complete 1 legion invasion on the broken isles, and complete 1 dungeon world quest on broken shore while command center building is active. Now my rep is at 8500+, only 3500 rep till revered. Since I did not make use of the darkmoon buff earlier, I have lost 10% of the rep gain. And I have never played the pet battle world quests, so there are lots of rep loss over past 2 weeks. If I have really done everything that is possibly done, I should be reaching flying rep now. Oh well, will need to farm world quests for a few more days.

I see youtuber is flying in now. I plan to come back when my freelance projects complete, am I going to have major disadvantage if I don have flying? mainly getting ganked because im on PVP server and my ilvl is not high because I don raid.

By now most people can fly. On PVP server being ganked while you are riding on the ground is definitely a possible issue, those gankers will probably kill you in two or three hits. The other disadvantage is you get to the world quests slower. And if you are leveling alt, flying makes it a lot easier and faster to do so, especially via the Legion invasion method.

If you already completed Pathfinder 1 though, it is quite fast to unlock flying compared to WoD. It takes me only less than 3 weeks even while not being optimal. Many people who go optimal approach unlocks it in 15 days or so. The key is to do all the quests you can on the new Broken Isle, and to complete all the world quests appear there everyday, and turn in all the war supplies for extra rep.