I have red root floaters and dwarf lettuce. I do not find maintenance difficult. I do weekly water changes and just grab a handful and toss when I am changing the water.
I've had some guppies that fall into the normal category but had rather rounded body shape. They kind of struggled to swim and I promised myself to never get any shaped the way again.
You need to do it a bit differently for shrimp. Put them in a container with the water from the bag, slowly drip tank water into the container for at least an hour (or more).
I don't think it is safe to use other than spot treating. I would spot treat just a little bit every day to give it a chance to break down. If you get too much in there at one time, I am sure the algae won't be the only thing dying.
looks to be unavailable now but I used this one. It worked well and has a place to add an airline so the food stays dry.
https://www.amazon.com/gp/product/B08CN6HWNK/?tag=ff0d01-20
I trim the roots all the time on my Anubias (all the really long ones). I do always leave about an inch or two. The roots on an Anubias are just to anchor the plant. They do most of their feeding through the leaves.
I have 3 tanks with lids and no problems. Dwarf lettuce and Red root floater. The only real problem I have ever had is keeping them out of the flow of the filter output.
Shrimp have a very small bioload so there can be a lot of them. Amano shrimp don't reproduce in fresh water. Shrimp populations will stop growing eventually.
I don't know much about Koi but I'm thinking for Koi that big, $50 is probably a pretty good deal even if the quality isn't great ( and I could not tell you if that quality is good or not).
I don't think anyone can tell you. It's very dependent on size and coloration. Just saying a type isn't nearly enough info I don't think. I could be completely wrong.