MySQL – How to Import Only Schema from Full Dump

Can't say about the size, but you could try and check for the last entry or the amount of entries in the dump and then check for the current last entry in your database. This might help you determine the time the import will take till it finishes.

The size of the imported data might even get bigger than the uncompressed 7GB, since the indexes are usually not contained in dumps but get built on insert.

As a sidenote: This is also a way to speed up the import itself: drop the index during import and rebuild it later on, this helped me several times to speed things up.

I haven't worked with PHPAdmin for a very long time, but it should be able to generate insert ... ignore instead of just insert. If my memory serves me well, there is a checkbox 'using insert ignore' on export/backup page.