that's one of few truths in pond keeping.
And obviously the number of fish and kinds can be kept in this size pond, even more. Growers and retail stores do it all the time. Have for years and years. You've already said you're going to test water parameters...that puts you way, way ahead of 90% of the "experts" who post in pond forums.
As you realized even in your first post, this type of pond is not a standard pond for this forum. Every pond forum has a specific and very narrow definition of what is a "good" or "proper" pond. Well, actually, every forum uses the same definition which is "a proper pond is a pond that is just like mine".
Which is unfortunate in this case because to me it would be interesting to hear about what your water parameters do and what actions you take to make it work and what you learn from any failures. I could learn a lot. Unfortunately I don't know of a better forum for you to post in specifically for container ponds. That's what this is called, a "container pond". There are lots of gardening forums that have threads on container ponds. Perhaps posting in one of those would be more fun than having to listen to "experts" tell you what the future holds.
Another option is to post in the section here called "Pond Showcase". In that section people can't make posts to your thread. Then later, if you have a specific question you can post in a new thread which will still get tons of "your pond is too small" but maybe you might get a few helpful posts on how to actually care for your pond.
Hope you can find some way to post. Send me a Personal Message if you post in another forum as I would like to follow this. I think container ponds are very cool, very interesting, and very surprising in how they react. I learned a lot about Water Gardens by keeping container ponds. One of
my fav ponds was 30 gal.