CSR is presented with a $2,000 cashier's check and a small non-next day check for $30. CSR places a new account hold on the cashier's check, but since this is a next day item, under the new account hold the first $5,000 must be available the next bus. day...so the $2,000 can only be held until the next bus. day, correct?

As long as the cashier's check is deposited in person to the account of the named payee (i.e. it is not a second party check) you must make $5,000 available next business day (which means you must make the full $2,000 available.)