I don't know exacly the way how to do it, but this is the way I would do it :

Download every file and open it in wordpad.
Purge your hitlogentries (they take up to mutch lines)
Make one file your main file (I suppose the file with the oldest posts in it
Compare every bit of table and add the missing lines in the main file
See that you have no duplicate numbers

create a new database and start uploading table by table.
Check if your database is working.
Finished (change the definitions in _config.php.

What's wordpath?

Is there any convenient way to handle the different IDs (since the numbers will be out of order/duplicated)?

wordpad is a normal texteditor on every pc.
It can handle langer files than notepad.

My desktop is OS X.

It's alright tho, I just imported the sql into my db under a different table name and played around till i got everything working. It was much easier to deal with inside phpmyadmin.