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?
1. Both are good choice but you don't invest in a stable coin. It's a way to retain the value of your profit.
2. That's too many and too much diversification. I wouldn't do that to be honest because that's almost going to get you nothing. You might earn with one pump from your 2-3 coins but then get a terrible loss from the other remaining coins. So, don't diversify a lot and get at least 2-5 coins of your choice, the ones that you have the strongest conviction of holding because you're going nowhere with that number of cryptos.
Lot of people think that holding too much altcoin would increased their chances of making profits from them because they thought there is likelihood of them soaring above expected but have also forgotten that those altcoin can as well increase their chances of losing them all entirely. Like you said having bitcoin as most priority coin and then includes few altcoin maybe 3 of them likely better, just as holding Ripple, BNB and Ethereum maybe he may decides to includes Tron and Sol on their portfolios these coin is enough to hold than going to hold series of coin that could easily create dying part for him.