Are there any limits on how many times you can buy/sell crypto on Coin base every day?
Op are you using Coinbase for your trades? Because most of the people don't use Coinbase due to their short list of trading assets available, the good point is on the centralized exchanges there are always Withdrawal Limits for trade limits I am not sure as I am not used to Coinbase. Your withdrawal or trade limit will be according to the tier = your KYC rank.
In general, Coinbase does not limit how much crypto you can sell to your Coinbase cash balance (USD, GBP, EUR, etc). Withdrawing from Coinbase will be dependent on the payment method you are using to withdraw.