niiice! also, what's so great about first grade ssj3? cuz I don't really see the point, if he can turn ssj 4... plus, can't goku turn in a superior level?
he can't turn ssj4 without technology, and first grade ssj3 is, due to his pride and his will to protect, his guilt and the fact that his body and spirit have entered ssj4 before, stronger than ssj3 normally. Meaning, if Vegeta were able to complete the ssj3 transformation, his power would be much higher than his current ssj4. Simply said, spiritual energy is stronger than the power of technology.
if he becomes ssj4 naturally, yes. If he uses technology, it will only increase strength a small amount and not as much as it would if it was natural transformation.