Well about bodyfat it'd we how the mirror complements with my strength gains. If I'm gaining a lot of strength and don't look anywhere near fat it wouldn't be a reason to stop. If I'm having some excess fat (with this I don't mean that my veins in my lower abs disappeared, this would be like love handles coming out) I'd add in some cardio for and tighten up the diet (A BIT) for the shortest time possible that makes me reduce fat and preserve strength. This officially is damage control.
One thing I'm gonna strive for right now is to gain a decent amount of weight for a year (20 pounds), make those pounds as solid as possible, and use some shortest periods possible of the year to eliminate any excessive fat gain, or maybe even be leaner at a higher bodyweight, who knows. I'm young, but when I dedicate to gain I can do it relatively smoothly, that's why I'm not hurrying, and FOR ME a 20 pound bw gain in a year is acceptable. Less than 10 is not, which would me evaluate if I'm not eating, resting, or training right.
I don't like to use numbers, specially if I'm not prepping for a contest, they can generate biases which can affect decisions in an undesired way. I'm not saying someone can't bullshit him/herself and say "bulking's alright, lightweight baby" and he just gained like 20 pounds in his bench, increased 30 pounds of bw and his muscles look like baby ass.