What exactly is the plan of Django & Schultz if everything went right

I dont get their actual plan to get broomhilda out ? they were gonna offer to buy mandingo fighter and in good faith they get broomhilda for free and then just take her and leave without buying mandingo ? in which case wouldn't candie send people after them for breaking the contract ?

No.

The plan was to buy Broomhilda, but they knew that Candie wouldn't give them the time of day if they came to him just asking to buy one of his (not so expensive) "ponies." So they talked about big money for the mandingo to get his attention. So the plan was to buy Broomhilda and make an agreement to buy the mandingo - on the condition that they would first have to have their own physician examine the fighter. So, they would buy Broomhilda and leave with her and with the promise to return with a physician to examine and then purchase the mandingo only to of course break the promise.

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so they break the promise by not returning with a physician ? in which case wouldnt candie send his men after them for breaking the promise by not returning with the physician ?
even if we use the analogy given by schultz to django earlier in the movie, if you buy the horse and leave with it under the promise that you will comeback and buy the farm...wouldnt they be suspicious ? wouldn't candie tell them to take her along with the mandingo after they return with the physician ?

Would he? I'm sure he'd be pissed about it, but it's not like he'd lost anything but time.

What reason would Candie have to be suspicious? Their plans went awry because Candie's sister noticed the way Hildy was acting and said something. Before that Candie and Stephen were both oblivious that anything was up.

I suppose if they were really afraid Candy would be pissed Schultz could have come back with a physician, and the physician would give a thumbs down to the mandingo, and then schultz could just not buy and leave, to make it look more legit?