I'm thinking this is a job best scheduled during an extended dry spell, if that can be predicted. That's assuming you do it the way you've proposed. I am looking at a similar project for my watershed adjacent to the pond and am envisioning a small dozer to do the excavating. I don't have the steep slopes of a pond to contend with, therefore I won't have to push dirt uphill. Based on your description, I'd rent the small dozer and pay a good operator to do the job and you'll probably get most all the dirt moved in one weekend.