You're on the right lines, but you must remember that using weights is not going to give you a "buff" look, as you put it, as women don't have the Testosterone levels to get really big, and in order for them to get even a good 140lb natural look, you'd probably be looking at a solid protein, 3,000+ calorie diet.
So don't worry. If you ate a moderate Protein, 2,000 calorie approx diet, you wouldn't get huge anyway.
I would suggest for now that you go for total body workouts, interspersed with your Cardio, so your body can get used to the Biomechanics of weightlifting.
Everyone does it. Starting off light, and working up a little each week, until they're lifting around 75-95% of max lifts after 4-6 weeks.
This is roughly how a weekly schedule could look.
Day 1 Weights
Day 2 Cardio
Day 3 Weights
Day 4 Day off
Day 5 Cardio
Day 6 Weights
Day 7 Day off
There are two reasons the off days are split like that.
1. It stops you training more than 3 days straight.
2. Having the two days off together, could eat into progress if you're sedentary for 2 days straight, so this prevents it.
With total body, you would be looking at compound or multi-muscle exercises.
This includes things like Rows, Deadlifts, Squats, Dumbbell Bench Press, Lunges, etc etc then potentially interspersing things like Bicep / Tricep stuff etc etc.
That could be done in your gym by an instructor, to help monitor technique and form.
Obviously you posted about Cardio in the Cardio section along with diet, so hopefully you'll find things to consider there too.

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A good body comes from hard work.