You want to start off slow when starting a new exercise. Are your heart, back, knees & ankles in good shape? Try 5 to start & add a couple every day. If they are in great shape try 10. If anything hurts after starting the exercise stop for a day or 2 & start with a lower number of squats. Realize you'll be sore but it shouldn't hurt. Good luck to you!
I would suggest 2 sets of 5 of easy weights. When I say easy I mean light weights to what your normally do. Because for a girl you probably want to be more toned than ripped. And toning is made from a lot of light lifts.
It depends on what your max weight is. Let's say your max is 130 lbs. I would start at like 75 lbs. and keep adding weight to my comfort. And balance your sets and reps. People usually start with 10 on their first set and decrease by 2.