I'm just coming to the end of my Taris part of my Kotor conversion and need help with the Space battle once the PC's escape with the Ebon Hawk.

I was planning or modelling the Ebon Hawk on the typical YT Model(I hope that's the correct designation) but i'm unsure on what to model the Sith fighters on. Would reskininng TIE's be too tough?

I have just got to grips with statting character encounters but vehicles is a whole new area for me.

Please help.

Four reskinned TIEs would be fine. That's the opposition at the end of Escape from Mos Shuuta, where the PCs have a YT-1300. I'd say it would be a fair balance, though if you think they might get worn down too soon you could always have them escape after X turns (possibly dictated by an Astrogation check?)

I was thinking that once they had madethe Astrogation check it would determine how long they have to last or beat the enemy until the jump to "Light Speed".

Would you suggest the TIE's be Minion groups or Rivals? How many would be fair do you think?

Two minion groups of two. It makes admin and targeting easier, while you can have one attack each side of the ship. It depends on how many players you have though. If they can only fill one turret though, I'd just have one group of two.