From what I’ve understand notifications are made for admin, am I right ?
Is it possible to send notifications to the author ?

Yep it works (for me ^^)

Maybe it can help someone :
I’ve change CSS to stick to the design but JS use file-selector to update UI so I’ve just put file-selector back and edit CSS so it don’t change the design.

> Leave file-selection class on the button
> Go to frontend-form.css and change line 15 to this :
ul.wpuf-form li .wpuf-fields a.file-selector{}ul.wpuf-form li .wpuf-fields a.file-selector:hover,ul.wpuf-form li .wpuf-fields a.file-selector:focus{}