Ditto what Matt says about the trainer. Years ago my husband gave me a gift certificate for our local gym (nice gift, huh!!) but it was the best thing! I learned what to do/not to do and I keep it very easy when it comes to abs.
After this last surgery I waited 4 months to start cardio and 5 months to start weights. I do a mixture of free/machine excercises and do not have any problems (but I don't do really high weights). My surgery was open so my recovery was lenghy.
I am afraid to do yoga...I know I shouldn't be but I am!!!! Good Luck.