Do NOT – I repeat – NOT – duplicate your clips. You will get duplication of conformed audio as well.
Just put the long clip into the source window, set the in and out points, then drag it back to the project window and rename it (it will have the same name as the original, so you really must rename it). Then move the in and out points and repeat for the next section.
Once you are done, you should be able to use each subclip as you are used to. Except that they are really not true subclips. You can trim the project with the Project Manager and it will create new sublips for you. Then you can get rid of the larger original file.