I think joining a slimming club or exercise class when nearing goal to help maintenance is a good idea. My Mum lost a lot of weight 6 years ago (not on CD) and has kept the weight off. She still attends a weekly class because she enjoys it and she says it's helped her to maintain.
I've been thinking of going to a Rosemary Conley class now l'm nearer goal.
When l first started the diet last March my CDC said l should aim for 10st or 10 1/2 stone, but l knew l wanted to be below 10st. It's maybe a silly reason, but l've always liked the number 29, so l decided on 129lbs (9st 3lb) which would take me to a BMI of 22.8 A lot can depend on your build though. I know at 9st 3lb l won't look overly thin.
My CDC has been great (she lives in my street, which is very handy, wish l had known about her 10 years earlier!) When l first started she said just take it a 1/2 stone at a time. When l began the diet l was 205lbs (14st 9lbs) and even getting to 10 1/2 stone seemed daunting, but the weeks and months go by and the lbs do drop off.