Depending on the boat and how low you want to weight it you are going to want 12' as a minimum depth. Anything less than that and it could diminish the wake from the boat. (ask for the technical speak as to why that is, if you want).
250' should be plenty wide, unless you have Randall Harris out there you not going to have a rider with a rope length longer than 75' which is 150' maximum width leaving 50' of run off on either side which is good.
For the bank have it sloped coming into the water. If its too steep coming into the water the wake rollers will roll back off the shore and just bounce back around the lake. nice and mellow and the waves just roll up on shore and go away. But you'd want a decent drop off after that so you minimizes the areas where a riding and accidentally run ashore and hit something with the boat. Turn islands at each end would also help the turn around rollers too.
A dock would be good for getting on and off the boat as well as a place for a rider to start from.
I don't know what kind of wind coverage you have there (trees, hills...) but if you don't have much I'd recommend you look into where the wind usually comes from for certain times of the year, based on that you can plant some trees that'll give you good coverage from the wind. idk what your place is like but would hate for you to get it all done and have the wind ruining the water condition everyday. And planting sooner would mean that they'd be well grown by the time you finished.
I want my own boat lake, and cable lake, and boat...