I am looking to take some profits on my altcoins after the next big pump.
2. Once I take the profits in stablecoins, is putting them on something like Blockfi to gain interest the best thing to do while I wait for another dip to possibly reinvest them?
For the security of your money purpose, keeping them in stablecoin is tge safest that's if you don't want them to be in fiats. Now ones they're in stablecoin, having them stored in your personal wallet is the next best thing to do. I don't accept the idea of handing them over to a third-party for storage or investment as you're simply putting back your money to the market for scammers to try stealing.
Many things can go wrong when your money isn't under your control, firstly you can get restricted from accessing you money or they get stolen through hack and now you'll have to rely on the operators of the service for compensation.