Not quite sure how EasyPopulate can ruin three months of work. It only updates the database, so rolling back to a previous database backup would sort that out.

The debug add-on produces a log file which it pops in the cache folder on your site and into which it pops any error messages generated by PHP. These help you to pinpoint the precise location and nature of the problem that has caused the blank page.

I highly recommend FileZilla. The FTP client has been very stable and very reliable for a long time and I believe that you will find that the server side of it is what is implemented on most Linux servers, so there's a good pedigree there.