Howdy there! Glad you really enjoy the gym, I'm a powerlifter in training, and I love weight training so much. I rarely do cardio these days, only for warm ups. (very important!)
You can lose fat doing ONLY weightlifting! I don't really diet that much at the minute. I'm pretty much eating freely (and I eat a lot!) and not gaining any weight.
I'm gonna keep this simple:
you will not turn into the hulk
1) Your body would require massive amounts of calories to create muscles. Bodybuilders eat 5k + calories per day.
2) It requires some serious training, bodybuilders dedicate their lives to their sport.
3) Women are simply NOT designed to create muscle like men. (not enough testosterone!) A lot of the women you see in figure comps are on hormones or steroids, and have SERIOUSLY scary diet plans to pull that off.
You should talk to a personal trainer if you can, get them to check your form for various stuff. If you decide to have a session, outline your plans to them from the off. There's lots of info online but there is nothing like getting someone with you to check you aren't hurting yourself. They can give you tips on what kind of exercises to start with.
Currently my training involves; Squats, Bench press, Deadlifts, Rows, Clean and press, and Snatches. Clean&press and snatches is stuff I do with my personal trainer, and the rest I'm doing within a plan called Stronglifts 5x5. Its a big strength training plan. The best place to start? Kettlebells. They be my absolute favourite.
Regarding reps - At the beginning it does not matter. Get the form correct. Get comfortable with the weight. I would say don't do more than 20 reps in a go (round the 10 range is usually good) and just get into the feel of lifting things. Don't go hard headed at the beginning and hurt yourself. Once you get comfortable lower the reps a bit. I usually do between 5-8 without any breaks, and 10 with kettlebell swings. I found really high numbers of reps just wrecked my body. Heavy weights with less reps get better results on your muscles with less wear on your joints! But keep it light until you get the form right and feel ok with the movement. Ideally get someone to check you over that knows what they are doing
With regards diet - ensure you are eating plenty.
Cambridge, and any of those low low calorie diets are NOT suited to lifting. It will hurt you and damage your body. Your muscles NEED food. I've seen and talked to too many people who are eating 1200 calories a day and doing hours of cardio, and not losing weight. Your body needs food to work. If you do calorie counting, ensure you eat your TDEE (thats your BMR + activity) every day you work out, and adjust it a bit lower for rest days. It takes time. Don't give up after a few weeks of not seeing results. Measure yourself. I would actually go as far as to say **** THE SCALES and throw them out. I haven't weighed myself in 6 months and I'm so much happier for it. Measure yourself. Take progress pics (even if you think they're awful, you never have to show anyone) and just enjoy it. This is a change of life for the better.
Make sure you warm up in the beginning, and do your stretches after your warm up (gets the blood flowing, cold stretching can pull muscles!) and just listen to your body.
I have so much functional movement its unbelievable. I am 20 stone. I can squat with my butt about 3 inches off the floor, and stay there comfortably for ages. I can lift 52.5kg of weight and put it over my head.
Also; have a look at these ladies competing in the olympics for some inspiration
Weightlifting - Women +75kg Group A - London 2012 Olympic Games - YouTube
Any more questions fire away
ALSO - important to note: I used to struggle with my eating. I felt like ASS all the time. I ate and nothing I could do would stop weight piling on at a shocking rate. Now I've developed my muscles I find I can eat what I want and the worst I do is a couple of pound a month, which I counteract with a bit more at the gym. And I'm not a gymaholic by any means lol