what type of pump? what type of return? how big should the filter be? what about a uv light?
I don't have a clue
If you buy a filter, make sure to buy one that is rated for 2000-3000G since over time they get clogged with leaves, algae, particulate, etc and if you don't want to be cleaning your filter every week but rather one a month, then buy larger than what is needed.
If you decide to build your own, here is a filter I built for a 600G pond that has worked great for years. Easy to follow directions:
http://www.interall.co.il/filter.html