You asked two questions, so I have had to cut it down to one according to enotes regulations. I think Leiningen is clearly shown to have many excellent qualities in this short story that indicate he is more than able to combat the stampede of ants that is heading his way. However, interestingly, you might like to think about how some of these advantages might actually be considered disadvantages, given the arrogance that Leiningen begins the story with.
To me, the most important paragraph describing Leiningen as a character but also in terms of his qualities is as follows:
Moreover, during his three years as planter, Leiningen had met and defeated drought, flood, plague, and all other "acts of God" which had come against him - unlike his fellow settlers in the district, who had made little or no resistance. This unbroken success he attributed solely to the observance of his lifelong motto: The human brain needs only to become fully aware of its powers to conquer even the elements.
Leiningen, then, has a good history of experience with such "Acts of God", he is determined, and he is convinced of the power of the human brain to defeat "the elements." What is clear as the story begins is that he is also an inspiring, charismatic leader, who is able to call upon the loyalty of his men, which is another vital characteristic for the struggle he faces.