Oh my sweet lil babies

springtaila decompose organic matter in the soil. they are a sign of good soil and they are very useful in a compost pile.
If the population is concerning to you, then you can control them with some nematodes or soaps. I don't think they cause a massive issue in soil based grows.

I'd leave em, they stay in the medium and will die out when it gets to dry. They feed on sugars as well so if your feeding any of that it is bloom their population.

Good Luck!

hold it together andn wrap some tape around it. in a 2-3 days come back and take the tape off.

the vascular tissue will fuse back together fairly well. the stem where it broke will be even stronger at that point than before. you may see some droopage the first day... you'll know quickly if it isn't healing.