Yeah, you can import PNG, just put all PNG files in a single folder and select a single PNG, it will use all PNG from that folder. The APP will try to auto-order, so the names should be 00001 00002 00003 or something like that.
Yes, it look good on pixel art, but you may need to do some manual fixes after. A good setup is setting the inner scale to X2 or X4
Alpha is fixed, if you export as a PNG sequence, gif output don't have alpha for now.