I think the minimum for tax reporting in some US states is around $600 income/year. If someone profits $599 or less (whatever the minimum cutoff number is by individual state) they don't have to report their taxes. Otherwise I think they're required to file.
The $10,000 number is the amount some platforms like crypto exchanges or casinos are required to fill out a tax form for and forward to the US government(if my information is correct) although there are supposed to be secondary measures in effect to catch tax evaders who attempt to avoid the $10k number in reporting. An example of this occurs in casinos where people might win more than $10,000 and cash out their chips in increments smaller than $10k to avoid having their winnings be put on file.
Capital gains taxes are a touchy subject. I think with stocks capital gains taxes are not incurred until after the stock is sold. If a stock is held(HODL'ed) longer than 1 year a lesser tax percentage is paid than with stocks that are bought and sold within 12 months. Uncertain as to whether bitcoin or crypto currencies need to be exchanged for fiat in order to be taxed in a similar manner. That's a grey area for me and one I would be interested in seeing someone more knowledgeable comment on.