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 see nothing bad in this, after all, you are investing. But I don't know what you mean by investing in the stablecoin, do you mean staking it?
2. Do you think investing in 20 coins is too much? Should I reduce my portfolio?
If I were you, I might limit it to just 5-7 coins/tokens. But you've done nothing wrong with 20 of them. Some people would have even more than 50 different coins invested. The difference is that you will be able to monitor and manage your coins/tokens better if they are limited, and if you select rightly, you will not miss out on profit-making.