There are people out here, like me, who would be tickled to death to have that much life in a tank. Aside from the hydra, they are all potential fish food items that can be cultured, though maybe not the flies.. they're a bit hard to manage
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If you happen to see some very skinny, very pinkish colour worm looking things that look like a series of S curves when swimming, you have Dero worms, which are one of the hottest new live food items around. Related to earth worms and one of the few aquatic members of that family. They are replacing brine shrimp in many commercial operations, because brine shrimp are getting too costly and hard to get. I'd kill to have some but can't get them in Canada, and it costs too much to import them. Seems US Fish and Wildlife has to inspect them first, for a tidy $200. or so, sigh.. so I can't get them here.
But I am buying lab cultures of most of those other creatures to culture myself for fish and fan shrimp food. Fan shrimp need tiny things to sift from the water, and tiny critters are also outstanding for feeding fry.
Hydra can't harm larger fish, but they sure can harm baby shrimp or fish fry who stray too close. They don't hunt, they just sit and wait, anything that comes close enough triggers the tentacles to grab and start closing and fires off nematocysts containing toxins to kill the prey.
Larger fish will eat hydra. I think gouramis will eat them, but don't quote me. I know they'll eat a lot of things other fish won't. Maybe you could borrow a gourami when the cycle is done, if hydra are still there. Do not crush or cut them, they will simply become more hydra. They're immortal, so far as science can tell.
Copepods and ostracods, as I've said, make really great live fish food. If you can transfer some to small tanks or jars and keep them going, you'll have amazing food for your fishies. Helps bring them into breeding condition like nothing else can. Once you add fish to this tank, virtually all these creatures will pretty much disappear.
If you want to limit importing more of such things, don't let water from plants or even new fish into your tank. Parasites can come with water, never mind pest species. This is why a quarantine tank for new fish is so important. It can save accidentally adding Ick to your tank, or some other parasite that will be a huge pain to treat.
Always rinse new plants very thoroughly in tap water at the very least. You can also dip them into weak solutions of either bleach, hydrogen peroxide or potassium permanganate, or even Excel. This will kill off algae, snails and most other pests. All are powerful oxidizers. The Skeptical Aquarist has some nice info on culturing, and I think on dipping too, as do other sites.
But be careful, some plants are super sensitive to being dipped. Vals are one that tend to melt, and might die, though they often come back from the roots with a bit of time. Moss can be dipped too. It may fade badly, but typically it recovers with some time.
Btw, that pic of eggs ? Almost surely from bladder snails. Ramshorns lay eggs in a neat little jelly crescent shape, it's amazing how tidy they are about it. Bladder snails are more of an irregular blob of jelly, as if they don't care how it looks. [
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Pond snails I'm not quite sure of regarding eggs, haven't seen any yet. Bladder snails are the dark ones that move quite fast, and seem to appear almost by magic. Most of us think they are pond snails, but while they may live in ponds, among other places, they are not true pond snails.
Pond snails get much bigger than bladder snails do, and bigger than ramshorns as well. I've yet to see a bladder snail that was even as large as an adult ramshorn snail, never mind a pond snail. They're just so darn successful, and though they don't really bother anything, most of us don't care for them unless we keep puffers or loaches that need them to eat.
