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?
2. Do you think investing in 20 coins is too much? Should I reduce my portfolio?
You should not re-invest your profits into another altcoin but you should
save your profits in BTC. Yeah, bitcoin must be the right investment to protect your profits. You may not prefer to be volatile with bitcoins but regardless of your assessment, bitcoin is the best opportunity to save for future. So, if you get any chances to profit from any altcoin then it would be much better to convert your profits into bitcoin, unfortunately I do not get any such chances to increase my bitcoin holding.
20 or more coins are okay but you need to watch them carefully for profit booking. I once held much bigger amount of altcoins but those were from bounty hunting and from other reward systems. So, how many coins you hold is not a criteria until you are able to track them and manage them.
If someone doesn't want volatility, they can invest in USDC and DAI for a while before the right opportunity to buy Bitcoin comes but at the moment I believe that now is a good time to buy Bitcoins, it will bounce back soon.
Btw I don't understand why would someone invest in 20 or more coins. It's very hard to track the price of these coins every day multiple times but even if you rarely check them, it's still not a good portfolio because there aren't 20 good coins in the crypto world, there are only a few that are worth the investment. My portfolio includes Bitcoin, Ethereum, Solana, Polygon and Cardano. I plan to invest in a few other coins but I don't want to exceed 10 coins.