A front wing isnt needed for stability, just for cornering speed. However, alignment is KEY here. If its off a little bit, it will lane veer over 120. I run 1/8 Toe-IN front and rear. Triple check those measurements and make sure camber and caster are the same on both sides. LF=RF and LR=RR. Rear wing with end plates helps out a lot as well.
Your 1/8th toe in recommendation...is that based on you sitting in the car, or with the car empty?
As others have mentioned, mine changes quite a bit depending on the loading in the car. With my wife and kid sitting in it (roughly the same weight as I am, combined), the front wheels toe out a bit, even though they are 1/8 in when the car is unloaded. So, I set toe-in with them sitting in it, and now when the car is empty, it's about 3/16 to 1/4 toe in at the front (rear stays constant at 1/8, roughly).
The car is flighty, mostly under power. I think taking weight off the front end, such as accelerating, and especially while accelerating AND hitting bumps, the thing is a white-knuckle terror machine. It will completely swap lanes before I can get a handle on it. Cruising on the highway is perfectly fine.
I originally set the alignment with no weight in the car, and it was even worse. Toeing the front in a bit seemed to help, but more work is still needed.