Large groups of zebra will remain in the Kalahari in March after their migration from the Boteti River so sightings of these are high. This also means chances of spotting predators targeting zebra will also be higher than other times of year, especially lions.
If you are looking to combine your Botswana safari with a trip to Victoria Falls, March can be a bit unpredictable. Water levels are high due to the recent rainy season however, if rains continue then there will be too much mist and cloud coverage to get good views of the falls.
That being said, it is not the best time to go to Botswana and it is better to go a little later in the year if that is a possibility for you.