Alfresco has some defaults metadata extratcors, it can obtain title, author, from word or pdf documents. This will be done automatically. If you would to modify something else, you will have to write an script and a file a part which should point to the metadata to be filled
The best way to do such type of massive upload would be configuring FTP on alfresco and upload them all. Take care if you have more than 1000 documents in the same folder because it will cause you some problems in terms of performance.
I would set more than one openoffice (jodconverter) port because you will enter in a deep indexing cycle and this will consume a lot of process