You may need to be signed off by your GP before you start the plan, OP. My consultant went through a detailed health questionnaire the first time we met, and certain health conditions required a GP letter.
As regards finding a consultant, I wanted a woman roughly my age, and someone who would come to my house, so looked only at female mobile consultants who covered my postcode. Then I read their webpages in detail, weeded out the illiterate slogan-y ones and made a shortlist of three. One had no free slots at all, and I went with the one I liked best on the phone of the other two. She's been great.
I told mine over the phone that I was vegetarian, and she brought a week's worth of different products to the first consultation, so I could get a sense of what I liked. After that, I ordered every week on Tuesday and she brought the products on Wednesday.
It really isn't possible to say how long it would take you to lose 51 pounds - they say roughly a stone a month, but I had initial drastic losses which then tailed off. I probably lost four stone in just over five months on 'Sole Source' - three products a day..
It's expensive, yes, but remember too that you are only eating Cambridge products on the first two 'steps', so no other food bills at all.