Hiya Omaha!
Answers in blue.
1. Very large healthy trees are in a few spots where the pond will be dug. Can I leave these there? Will they survive in a couple feet of water?
- The trees will die, but a few of them left in a small bunch makes for some great fish holding structure. They will also be great habitat for birds like purple martins, woodpeckers, owls and wood ducks.2. The ground is relatively level. Is it necessary to create a dirt/clay barrier between the crop fields and the pond area?
- I'll let the dirt experts answer that one, but no that you mention you will have crop land surrounding the pond, I do want to throw in a suggestion to establish a large grass buffer strip around the entire pond to help cut down on silting and fertilizer and herbicide leaching.3. I don't believe we'll be able to create an inlet pipe from the creek to the pond to fill as the elevation of the pond will be significantly higher than that of the creek. Keeping the options of pumping or naturally filling in mind, would a spring be beneficial if we were to hit it when digging? I've heard conflicting reports. On one hand, I understand spring water is a very healthy source of water. However, with the creek level being so far less than where the pond will be, would the spring only allow the water level to rise to a certain point, much lower than what I would want?
- Springs are often a major issue. They can act as a faucet and as a drain. 
4. What plants should I consider? I was reading through and saw some great reviews for vetiver grass, but this can't freeze (obviously something that happens a few months every year here). Are there alternatives to this? My cousin is a forestry major and suggested a type of wheat. What types should I look for? Also, of the 9 aquatic plants I detailed in the above outline, which are good to consider and are there any others that I should consider?
- Water willow is excellent for shoreline protection and makes excellent hiding areas for fry. Chara, I probably wouldn't worry about adding chara. It'll most likely show up quite quickly on its own. Your two Iris selections are excellent. They are a great marginal. Pickerelweed is another great choice. Ducks absolutely love the stuff though, so keep that in mind. Note: I currently have all of the ones I mentioned in my pond. I am planning to add more water willow and Iris next spring. I may have some extra plants I'd be willing to donate to your project if you are interested. I'm north of Kansas City.5. I've read for a small pond, you can easily create too much structure. How much is too much? I love the ideas I've found throughout this site and think this part of the planning will be one of the most fun but I don't want to overdo it.
- If I were you I would leave a nice bunch of mature trees in a spot of the pond. That will leave you with some nice initial structure.6. I was unable to find plans for constructing a floating dock on a budget. Does anyone have anything like this or a link to this?
- There are some plans for using 50 gallon plastic barrels for floats. As long as the floats are positioned correctly, you'll end up with a pretty stable dock. I'll dig up some links later(they are somewhere in my 10k+ list of favorites), and I'll replace this text with the links. EDIT: Here's a link I found: http://answers.yahoo.com/question/index?qid=20070917142345AALAyNt
7. Is there a particular type of sand that I should consider for the small fishing area and what size should I make it, keeping in mind the entire area of the pond is approximately one acre?
- Any particular reason you want sand for a fishing area? Maybe you meant swimming area. At any rate, I would be more apt to put pea rock down, but that's just me.
