Realistic goals

I have just started going to the local gym to aid my weightloss and increase my fitness. My aim is to work on cardio before adding weights as I have several issues with my back and my knees which mean I have to be very careful.

I started with a test on the treadmill that put my Performance indicator at just 10.

My program was set:

Treadmill 20 mins (3.5 - 8.5 speed  and 0.0 - 5.5 gradient)
Bike 10 mins
Reclyner bike - 5mins
Arm rotator - 4 mins
Treadmill 8 mins (3.5 - 8.5 speed  and 0.0 - 5.5 gradient)

My first session last Thursday burned 273 calories and gave me a performance indicator of 11
My second session on Friday burned 294 calories and gave me a performance indicator of 12 (I manually over rid my program in places to increase, speed, resistance and gradients)
My third session today burned 302 calories and gave me a performance indicator of 12.

I have added for the next workout - 5 mins on a wave machine exercising my outer thighs and 5 mins on a sit down chest press at 10kg.

What I am wondering is what is a realistic goal to have for a performance indcator (I am thinking about 30) and how long should it take me to get there? (I am thinking 1 or 2 points increase a month)

Also being very figure orientated I have set in my mind to try and increase calories burned at each session.... so far so good... is this okay?

Thanks for any advice.