Looking at the Datta sheet that comes with the ship... I'm assuming that the rear half of the ship is the auxiliary fire arc .. Am I correct?

No. The diagram in the insert is very confusing. What it is doing is shading the auxiliary arcs and leaving the primary arc and the out of arc area normal, but that makes it look like the primary arc and rear half are bolded, so a lot of people think it can shoot behind itself.

What the 666 actually has are 2 auxiliary arcs, one on each side of the primary arc, that allow its primary weapon to fire 180* forward.

With is maneuver dial that makes him pretty weak

Stick a feedback array and Engine Upgrade on him. Then there's almost nowhere things can go to get out of both your arc AND your feedback zone. Doubly so if you also take Daredevil.

With is maneuver dial that makes him pretty weak

it's not YV being weak, it's just YV being "half PWT" with even PWTs out of favour.

luckily it has Amoralo Eval for DAMAGE OUTPUT

It's a ship with a lot of options. You should slow roll as often as possible and you don't want anything getting behind it. The three crew allow a lot of options. I'm currently enjoying Lats Razzi with Weapons Engineer and the K4 Security droid. The hard part is making your squad with something equally threatening so that target selection is difficult. The YV-666 generates agro in direct proportionate to it's size (the lone itty bitty green defensive dice also makes it a good target).

With is maneuver dial that makes him pretty weak

it's not YV being weak, it's just YV being "half PWT" with even PWTs out of favour.

luckily it has Amoralo Eval for DAMAGE OUTPUT

But unlike a turret, the YV's wide arc doesn't trigger Autothrusters but does trigger things like Tactician.