Thanks for writing. My own pond is close enough to the house so I can sit on my back deck and watch the fish swim and the birds drink so when you ask how close it should be I can only advise to choose the best spot considering sight-lines, elevations to avoid flooding or unwanted pooling of water during rains.
I like a maneagable size for my fairly limited desire to do much work and maintenance on my pond. I want to feed my fish and grow some plants and enjoy the sounds not create another job for me and my wife!
Let's get to costs:
1. Aeration: I'd look at $800 to $2000 depending on how much you want to do yourself: Here's some parts and system prices
2. Chemicals: We try and avoid any harsh chemicals, instead using safe and natural blends of bacteria and enzymes. You might need $200 to $1000 per year depending on your pond and how it's built and stocked. More pricing and variations to consider for additives
When I was working for a pond supply and construction firm we did it all; from planning to construction and then supplying aeration etc. First of all, from what I've seen over the last 18 years, you should expect to follow a few basic steps: choose the site, verify the site will hold a pond and keep water, evaluate the environment and watershed, have a plan, know what sort of pond you want.
Contact a few local pond builders and ask for some pricing. We always told our clients that a finished pond would cost in the area of $1 per square foot...since a 1/2 acre pond is about 22,000 square feet we would often ballpark $22,000. Of course this depends on terrain and how much landscaping, if any, you want to do.
A one acre pond can cost $45,000 if you are using the dollar a square foot formula but it can also be done much cheaper if you have access to the tools you can do your own research and build your own pond. A good contractor will want to do a soil test to ensure the water table and soil structure are correct. There are some very good books available and are invaluable if you to build and maintain a healthy pond. The cost of a few books can save thousands of dollars on your project.
Pond Building Books & Guides
The depth you want to dig depends on if you are having fish, if you have natural springs feeding the pond, and if you are in good clay or soft sand and need a liner. As I've said before a pond that is natural will want to maintain a 2 to 1 slope so no matter if your contractor says he can dig a 30 foot pond that is 50 feet in diameter it will soon be only 15 feet deep based on the natural laws of physics.
Of course we did incredible landscaping and made the pond look like a totally natural pond with rock features, lovely embellished banks and natiral plants along the shoreline. Many contractors will quote low and dig you a hole that will turn into a muddy mess.
Be careful and ask for references! Your pond, once built, might look rather poor for a couple of years until the vegetaion takes hold and depending on many conditions that we often consulted on. Aeration in a 1/2 acre pond should cost no more than $2000 and is usually not less than $800. Again...it depends on who you ask. It is best to ask an established firm as we've seen the internet clouded with many so-called experts!. For chemicals...if you build the right pond you won't need any!
Perhaps a natural bacteria would help but chemicals can lead to a dependance and even more problems. A pond is a living eco-system and should be treated differently than a swimming pool! I've worked on many ponds and suggest you do your homework and ask an expert before giving anyone the mandate to "Dig In!"
Have fun! Owning a pond is a wonderful thing!