This quesiton again...

I know the whole "am I eating enough?" question comes up all the time on here. And I know I can look back and see some answers, but I'm asking again anyways, and sorry if this post is too winded. I've "dieted" successfully all the millions of times I've done it. I've done it by counting my calories on MFP and running on my treadmill for 30 min, usually 5-6 days per week. I've lost about 30 lbs each time I've done it. Then I stop exercising, start eating crap again, and boom, I'm back where I started. So that's gone on forever it seems. This time, just last weekend, I decided to join the gym so I could not only do cardio, but do some strength exercises as well. I want to lose about 40 lbs, so its not DRASTIC, but I also want to get fit and healthy and build muscle and lose inches. I do about 30 min of cardio to get started, and then I have done legs, butt, etc one day, and arms, back, upper body the next. I plan to continue like this, again working out 5-6 days per week. I am not at the weights yet, I'm just doing the machines in the gym, like the circuits, I think they call them. Again, just started this week. My question now is I have my calories set at 1200. Just b/c that's what I've done since I joined MFP, when I am counting my calories I do it at 1200. But that was when I was strictly doing cardio. I don't know if I need to raise that a bit since I am doing some machines now tho. I know the whole "you need to fuel your body" thing, and "starvation mode" although I can't imagine myself starving. I guess I'm just asking for suggestions from people that do the machines. I don't know how much they may or may not burn. I haven't gotten a HRM yet, I plan to, but just not yet. Any advice for this "newbie?"