i have a 120 horde, i have completed all of the zones and unlocked wq.

if i transfered to alliance would i have to complete all of the zones again? or would that transfer over aswell

and do horde reps transfer to alliance reps

Considering the horde and alliance zones are completely different you'd prolly do em again.

I think you should be able to do them again, but you will have the achievements you have completed, so you'd get flying for example if you completed it on horde

it's likely similar to past expansions where everything faction related is reset

I did this exactly and reps changed, but didn't reset, I still technically have the horde area done just need to do alliance but I have wq unlocked before I transferred so I just had to do the starting quest to get my pally to the area, probably have to do a few more to get to the other specific areas so I don't have to walk the whole way

^^