There are many great products out there if you nose around. A few points to consider in your design.
UV - if you want really clear water this is a must, the fish really don't care as much as the keeper.
Skimmer of some kind - pollen, leaves, algae can all make the surface look pretty bad. If a skimmer box doesn't suit you, then have the water spill into a smaller pond and set your filter intake there.
Easy to service prefilter - the first point of entry should be some form of corse sponge that you can remove and rinse easily. This will be 50% or more of your cleaning of solid matter. Keeping this out of your system extends the service of watever filter you have down the line.
Keep in mind your choice of occupants. Koi are dramatic but they are quite a bioload. Commets are more subtle but less of a load. I had commets spawn in a 350 gal. pond in NJ, for a few years. Unfortunately I've since moved and miss my pond (almost a puddle) dearly.