Welcome. While researching my first pond build(after I dug the hole) the first thing I learned was to do your research(atleast a years worth) before you dig. At first I thought that was crazy but I now know its the best way to approach this. First you need to know what you will be stocking in your pond. Goldfish and koi are to different pond setups. Goldfish will do fine in a koi designed pond, but koi won't fare as well in a pond designed for goldfish(unless it is set up as a koi pond), if this make sence. Koi grow larger then GF so they need more room. 3' should be the minimum depth for koi. Also koi will destroy most plants in your pond so if you want koi keep that in mind. Next step is you filtration, more is better, you want at the least 1 turn of the water per hour, 2X is better, 3 would be great. You want a bio filter of sorts(lots if DIY ideas here).You want to design it to handle your water turnover rate. Naturally you cant have to fast a turnover for your bio filter but you can adjust this with valves. I have 3- 55 gallon doc style filters with @4000 gallons going through them. Last thing I will mention is try to avoid the temptation to put rocks in the bottom of your pond. After a few month it will start to harbor bad bacteria under the rocks and you water will turn bad in a hurry.
