Can I have more than one AND in the WHERE clause?
Yes. In fact, all the operators can be used multiple times. An example would be
SELECT SALARY FROM EMPLOYEE_PAY_TBL WHERE SALARY > 20000 AND BONUS BETWEEN 1000 AND 3000 AND POSITION = 'VICE PRESIDENT'
What happens if I use single quotation marks around a NUMBER data type in a WHERE clause?
Your query still processes. Quotation marks are not necessary for NUMBER fields.