Keep in mind a dozer is the most expensive piece of equipment there is to maintain. Its not if its going to break but when and how many times. This is especially true on used machines under $30k.

Excavating a pond with a dozer will result in a large, shallow pond. Its simply not possible to push dirt below the water table with a small machine. Get a D8 and now you can do some digging. You will also be burning 40 gallons per hour of fuel.

As a backhoe owner I will tell you they are not pond digging machines. They are a great jack of all trades machine but suck at pushing dirt and are too slow at digging for pond work.

Dozers are awesome but messy. Pushing trees over is fun, but cleaning up the mess and making it look decent is 10 times the work. Using a backhoe to go through the woods and pick trees out of the ground is slower, but a LOT less messy than a dozer.

Buy a excavator in the 320 Cat size range and a backhoe and you can do anything. Sell the excavator when you are done and keep the backhoe to make things look decent