lazarus, in contrast with delphi, uses a dynamic "known path" system. Each project creates its own search and output path list by adding in the project the required packages. In your case open the package select "add\new requirement" and add the packages required by your component I think that you need at least lcl and lclbase. After that try to compile and see which units can not find. Find those units pacakges and add them to the required packages of your package.
Now as for the duplicate compiled files, if its about your files then always answer yes, let the IDE clean up those duplicates for you, less headaches down the road.