New to this!

 Alright, so just before surgery I got set in a routine doing cardio, now after surgery I want to add in weight training.  I went to the gym yesterday, working my butt, off but I had no idea what I was doing!  Any advice?  I am sore as heck today, so I must have did something right.  :)

I am down 70 lbs since I started my journey.  But concerned about muscle loss, I want to prevent that and add muscle.  

Muscle loss is unavoidable when you are losing weight so rapidly and are in a stat of Kitosis... Muscle weighs more than fat so if you add muscle, you need to up your calories, and will likely gain weight... My suggestion would be do strength training and continue with Cardio... You will eventually gain muscle back after you lose the weight, but there reall is no way to gain substantial amounts of muscle on a 600-1000 calorie diet...

You probably have a lot of muscle anyway. Carrying around all that weight builds it up.

Then, as we lose weight, we don't use that muscle so the body takes it for energy. Strength training tells your body "Hey, I needs those" and so it will go after fat instead.

Well, that's a bit simplified... you'll probably still lose *some* muscle, but not as much as if you don't strength train.