How can one know if their question has already been answered before sending it, in order to save effort, and is it possible to send more than one question per day?

May Allah reward you for your good opinion of us. The fatwas we provide are but the humble efforts of one who possesses little. You can examine the "Thematic Display" before submitting your question, as you might find a previous answer similar to your question. You can access it from two locations: at the top of the page under the title, and on the right side of the page under "Membership." You can also search by keyword or keywords. You can send more than one question daily as long as submissions are open.