Decorative bricks and press board make nice shelves if that is what the budget dictates. If you need to order furniture, Highsmith or Demco have very nice furniture. Perhaps there is someone in your community who can build you some furniture. This may take some time, however. Lighting is very important in your library, especially if it is used as a reading area.
Windows facing south also bring in the warmth from the outdoors.
An automated circulation system will cut down on a lot of the paperwork it takes to manage a library. A circulation system will run your overdue list, keep count of the number of books in your system, keep track of the number of books checked out that day and is a wonderful tool to use when inventorying your books. The system I use is from Follett. Not only does it tell me how many books I have in each Dewey number plus fiction and everybody books, but it also tells me the percentage of each. Follett offers a computer card catalog.