1. Is it okay to rotate my profit into another coin, or should I invest it in a stable coin or leave it in USDC?
I will not rotate the entire profit, just the capital, if you also include the profit then you can lose everything, so just rotate the capital.
2. Do you think investing in 20 coins is too much? Should I reduce my portfolio?
This is too much in my opinion, because you might only break even because even though you get profit from the 20 coins, some of them make a loss so you don't get anything. It's better to focus on just a few coins, even just Bitcoin is much better because cryptocurrency is full of speculation.