Thank you very much, Waterbug for your great questions and time
You are welcome. But you may not be thanking in a little bit.
I condensed your wish list.
Koi, 5 to 10 fish, $1000 budget
Pond budget $1.5K max.
Lots of plants.
Raised pond, wood exterior.
Rocks inside the pond.
***Main interest is the fish. Raising, treating.
Pond size 10'x3' and 4' deep.
That's a huge help. Now we can start getting into reality so you get the things you really want. Everyone wants a small pond with lots of fish and almost no cost. Guess what?
Let's start with the photo of where the pond will go. 3', is that the width of that flower bed? Because a pond has pretty thick walls. If the bed is 3' the pond will be 2' or less. So when we're talking about smaller ponds it's important to start nailing down the exact size. In larger ponds tweaking a foot or two is no big deal. That can drive many other things.
So if the inside of the pond ends up being say 9'x2' 4' deep, but never 100% full so say water depth of 3.5' that's about 475 gal.
You want 5-10 Koi. Koi get to be 24-30" when well kept. Turning around in a 2' wide pond is difficult. So there's that.
There is a saying in Koi keeping that you can keep Koi in a bath tub given enough filtering. I would add experience too.
The standard response from 99% of people is 475 gal for 5-10 Koi is way too small. And I agree. However, you said you are highly interested in the care of Koi, breeding, treatments, etc. To me that means you'd be OK getting a microscope for diagnosing problems, hospital tank, the whole 9 yards. Well, that could actually fit with keeping so many large fish in such a small space. I mean it forces you to become what you want, a top Koi keeper. Few people in the world could pull off what you would be attempting. So I'm not going to give the knee jerk response and say the pond would be way too small and instead give a general idea of what this might take.
At the very beginning you said you wanted the lease maintenance possible. The pond you want would be the highest maintenance possible. You would have to test water almost daily. And lots of tests, not just the standard stuff. Some of that equipment is expensive. A small pond is easier to keep clean, so that's a plus.
I think you mentioned having a bog. I love bogs in a Water Gardens. But they in no way shape or form should be considered a filter for a high fish load pond. Bogs collect waste which sits in them and rots. A lot of waste. In this forum bogs are very popular, people say they make their water cleaner than drinking water, zero DOCs and whatever else to make bogs sound like the greatest filter ever. Go into any Koi forum and say bog and they will set you right. Waste collecting in a pond is never good for water quality. In Water Gardens that's not normally an issues at lease for the first 5-15 years. In a high fish load pond most of the waste will be fish poo which is as much more potent type of waste.
Plants are not your friend here. In Water Gardens sure, plants are the main focus. But in a high fish load Koi Pond plants are not an option. I know in the Water Garden world people consider plants to be great filters but that's way over hyped...because plants are the focus. Plants can have some benefits, but they also have some down sides. In a super high fish load pond like yours the downsides far, far out weigh the pluses. They add more waste than they remove (true in Water Gardens too, but that's OK those ponds can handle the waste).
I suggest a separate pond for the plants, I think you were thinking that too. But don't connect the two. Separate water. The issue is DOC (dissolved organic carbon or compounds). Just a fancy term for small bits of organic matter. It actually is just a definition of the size of these bits, not the amount of decomposing organic matter. But really all decaying organic matter is a problem in super high fish loads, dead fish. No big problem in low fish load ponds.
So plants have to be separate. Other organic stuff we need to keep out, algae. UV filter is required for your pond. Macro algae is OK, but has to be brushed maybe weekly if present. More maintenance.
That leaves fish poo. In a low fish load pond it's no problem. Super high fish load it is a super high problem. A bottom drain and gravity fed Cetus type sieve filter is a requirement imo.
Serious bio filtering will be a requirement. We're talking reall Bakki Shower filters and a lot of them. These are large and very noisy so you'd need to find a spot for them. If you had to moving bed filters could work too.
You should consider a 24/7 water changing system. This is where city water is dripped into the pond, 10% of the pond volume per day. An overflow takes away excess. That will greatly help with water quality. Chlorine isn't a problem because of the slow addition.
You need to keep a running hospital tank. Normally these are larger than your entire pond and fully equipped.
Now for the big bummer. The sieve filter alone is in the $1200-1500 range. There are cheaper/smaller options, some that don't require a filter pit. You can go DIY and greatly reduce cost. But these don't work as well, need more space, etc.
On the fish budget...you clearly want decent fish and already understand what they cost. I suggest not buying expensive fish to start. 5-10 Koi in this size pond is a very difficult under taking. The smallest thing can kill the fish. Power off for an hour, dead fish. In order to learn you will be going thru a lot of fish. Best not to waste money on expensive fish. I would wait until I could raise 5-10 cheap Koi to say 5-6 years old. Raise them just like you would expensive Koi. There is no difference in the raising practice for cheap or expensive. After you have 5-6 years of successful experience (which may take 10-15 years) then buy expensive Koi. Unless of course you win the Lotto in the mean time.
Hopefully that will help you focus more on your goals and maybe reconsider some things. Planning is cheap, fixing is expensive.
