i have to agree with Sean on the a native marine. But we are talking ponds so i shall stick with that.

first the problem i can see because we are talking native fish all infections diseases and parasites are already in the area. first on capture they will need to be wormed at this stage the answer is simple this is done in a tank. but once introduced to the pond this is out of your control thus this pond will need regular treatment for worms and the cost involved with treating a pond of this size. And why you will have birds, frog and newts coming from infected areas.

On the plus side the viewing port is a very good idea maybe at the side of a Italian sunken garden or as a raised area. if the pond is planted with cover in this area fish will feel safe and use it thus visible as we are not viewed as much of treat from the side as we are from above.

I am sure others will point out other pros and cons. And i for one am in favour of the growth of home grown tanks and ponds we should remember a lot of imported pond fish started as a food source and over time became the beautiful creatures we have to day! And what hidden beauty is hidden in our plain natural stock!?!