Thank you both for the replies...and the links. I think he will have about $30k in capital gains & dividends and then $4k earned income.
EITC has a hard cliff: if you have investment income of $3500ish you are not eligible at all, full stop.
Providing 50%+ of his own support has different definitions for dependency vs credit qualification. For at least one of them he must provide more than 50% from earnings, not just investments. Read the details closely. I'm always confusing the different rules.
He will still be considered a dependent for financial aid purposes (even if he is not for tax purposes) unless he is over 24, in grad school, married, has a dependent, member of the armed forces, etc. His income and assets will be reported on the FAFSA and added to yours (after minimal "protection" amounts are removed). Google "EFC formulas 2018-19" to get the pdf and do your own calculations. I don't believe the newest version for the upcoming filing is out, yet, but you could try 2019-20 too.