Welcome to the forum and to Keystone RVing. We're happy to have you join us. There is a tremendous volume of information available to you by using the search function located in the top blue bar of every forum webpage. If you click on SEARCH and type in propane use, you'll get a number of results to help guide you to answers to your questions.
To get you started, here is one link to the same question you have posed:
http://www.keystonerv.org/forums/sho...hlight=propane
To answer your question in very short form, if you get a week out of one 30 pound propane tank (7.5 gallons) you're doing very well indeed.
As for the beep, try changing the battery in your smoke detector.
Again, welcome to the forum.