You should probably spend some time in the Help Center understanding how Airbnb works before you do anything. These are really basic questions easily answered there.
No, there is no posting board where the hosts come looking for you. If you have specific needs, you need to craft an email, find properties that you are interested in staying for the dates you need, and inquire if the guests can support your stay - especially if you have some unique requirements. Read the profile listings in full to get a real understanding of what is being offered at each location. When you enter the full number of dates you need, the price should be for the over night accommodations. You should be able to see the break down of charges, including taxes, cleaning and fees. It won't, however, show you the charge of any other items the host charges which will be noted in the listing. This could include additional fees for using the pool, internet, pets, breakfast, rides, or any number of add-ons you will pay for via the Resolution Center.
