Please help answer my fitness questions

Here's a newbie help post which includes links to helpful info such as sexypants (go read it now) ((seriously, now)), setting realistic goals (weight, calories, macros), accurate food logging, exercise basics, motivation...
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I do most of my workout in cardio mode because I have a lot of weight to lose all over (at least 100lbs) and I heard cardio is the best

Cardio is the most effective way to burn calories, and your metabolism is elevated for a couple hours afterward, but weightlifting is essential because you want to maintain the muscle you do have. It's much harder to get it back than to keep it.

Also, even though the calorie difference isn't huge (2 cal vs 6 cal), muscle does burn more per pound than fat. So the more muscle you have/keep/build the more you burn _all_ _the_ _time_.
If you're running behind some day & only have time/energy to do one or the other, do weightlifting.
Ideally, do cardio at least 5 days a week and weightlifting 2-3 days per week.
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i burn at least 300 calories on the treadmill in my time range... is that enough cardio to lose weight along with this mfp diet?

Stop thinking of this as a diet. Diets are temporary. Once you go back to your old eating habits, the weight will come back. You have to make a change in your life, that will last the rest of your life, if you want the weight to stay gone.

If you've set your MFP activity level to "inactive", and you log your exercise, it will be the most accurate for calories.
As long as you eat less than your body needs, you will lose weight.
It's easier to do that by controlling calories in than by exercise.
My doctor & dietician told me that I shouldn't eat back exercise calories because
a - most people underestimate what they eat and
b - most machines (including MFP) overestimate calories burned.
For most people, most of the time, those errors cancel out.
If you're really hungry at the end of the day once in a while, eat 1/3 - 1/2 of your exercise calories for a snack.
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idk how many reps of and sets of each strength exercise to do and Idk how much weight on these exercises I should set it to... I heard if you do too much weight then you build mass (and obviously I don't want that lol) I just want to help target certain areas to lose weight (like my arms and chest and tummy)

See the exercise basics blog post I did.
Recommendations are taken from the American College of Sports Medicine's book "Resources for the Personal Trainer, 4th edition".
(IOW, I don't just make this stuff up.)

Yes, you do want to build muscle mass if you can (which is hard for women, and nearly impossible while eating at a calorie deficit). Probably all you'll be able to do is maintain what you currently have.
The calculator just below says that as I've lost over 80 lb of fat, I've gained 4 lb of muscle. I think it's measurement error, and am happy simply to know that I haven't lost muscle.

You're not going to bulk up if you're a normal natural woman with normal female hormone levels and you're not taking steroids or testosterone.
One famous female weightlifter who is a member here on MFP is SaraUK2SF. Go have a look at her pictures. She's not bulky, is she? Looks pretty good, right? She works very hard at weightlifting & is very very strong.

Here's a body fat calculator, so you can know where you're starting (how much fat, how much lean body mass). It will also tell you the healthy body fat % ranges.
http://fitness.bizcalcs.com/Calculator.asp?Calc=Body-Fat-Navy

Here's an illustrated guide to weightlifting exercises. (Ignore the spam on the site about buying supplements, etc. Just use the free tools, including the one to create your own workout.)
http://www.bodybuilding.com/exercises/
Work both sides of the body - situps & back extensions (and torso twists), bicep curls & tricep dips, leg extensions & curls, hip abduction & adduction, chest press & row.
Does your gym offer personal trainers? The one I go to has them for free, but it would be worth investing in a session or two to learn how to safely use the equipment and have her/him write up a personalized exercise plan, plus teaching you how to make it harder as you get stronger.
Here's where you can search for people in your area who are certified by the American College of Sports Medicine:
http://members.acsm.org/source/custom/Online_locator/OnlineLocator.cfm

You can't target areas to lose weight. Your body will lose where it decides to lose. It's genetic. If your female relatives are pear-shaped, have big butts & thighs, that's probably the first place you'll gain weight & the last place you'll lose it.
What you can do is build the underlying muscle so that as you lose the fat you will be toned & firm.

LOL! Thank you.
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This...

All of the above is "spot on" advice.

BTW:

You're not going to bulk up if you're a normal natural woman with normal female hormone levels and you're not taking steroids or testosterone.

Those aren't the kind of steroids you get from the doctor when you have a skin problem (I've taken them for poison ivy) or maybe an asthma flare-up (BTDT). Those are metabolic or corticosteroids. They block chemicals in your body that are involved with allergic reactions, including inflammation. Most likely (unless you're allergic) the worst they'll do to you is make you hungry.
(And there are some natural and important chemicals which are included in this category, things which keep your body running right, like vitamin D, estrogen, cholesterol.)

Muscle-building steroids are completely different. Those are anabolic. They're related to male hormones, and they promote muscle & skeletal growth & other masculine characteristics. These can cause high blood pressure, tumors, shrinking testicles in men, facial hair in women.