If you have done everything in the order that Jason described, then the files ending with '_new' can be deleted.
If it were me, I would leave them intact just long enough to see the imported data showing up in the admin pages, then I would go ahead and delete them. There's no reason why they can't sit there for a bit, until everything is up and running smoothly.
I'm not the person to ask about syntax errors in PHP, but if you were to zip and post the page here, someone will spot the error and post a solution.