you have almost the same situation I faced last Christmas. I was 240 lbs and 5'11" Fortunately I had many years experience of cycling and being fit so I knew it was just a question of cutting down severely on the calories and gradually building up the miles on my bike .
I spent some time planning my program beforehand so that I already had some targets and direction . This helps with motivation and monitoring progress.
I mapped out 3-4 hilly routes around my home of about 5-6 miles each.All of the loops reversable so I ended up with quite a few differant loops . I figured also that short routes would help keep me focused and the hills would give me a short but intense workout.
When I first put my lycra on I have to say I was very embarrassed at my huge belly and from the rear view I looked like the Michelin man .
I always start with 2-3 miles flat warm up round the village then finish with 3-4 miles hilly loops with plenty of downhills to follow the uphill bits.
Within 3 months I'd gone from 30 minutes to less than 25 minutes for the 5.7 mile hilliest loop and my legs started to get some muscle definition. My lungs no longer burned nor my legs turn to jelly and I felt great mentally too as I lost 5-6 lbs.
I kept a food diary and recorded the calories of every single thing that entered my mouth including fruit drinks etc. I was amazed to find that instead of being on about 1500 calories a day I was actually consuming near 2500 !
By changing certain high calorie foods for low calorie options I soon got down to about 1500-1800 calories a day and the weight started to fall off.
First to go was by gross fatty flabby double chins and cheeks (face) then my waist and breasts also .
I wanted this to be some motivation to you and to say that cutting your daily calorific intake will lose you weight 10x faster than any exercise could. Exercise will help with improving cardio vascular fitness , toning muscles and making you feel more energetic and positive. Good luck