Soldering that chip was surprisingly easy, once I got it aligned and two pins soldered in place it the rest was a breeze. I used acrylic paint as a solder mask, actually I painted it after soldering, just to keep the traces from rusting.
I'm printing the masks on inkjet tranparency paper, but I'm having problems with that because when the ink dryes it craks leaving very thin lines, in fact I'm surprised that such thin lines remain after etching. So I have to use a marker to cover the cracks, but still some remained on the mask and that's what causes those little spikes along the traces.
I also made a little test of the film as solder mask on a bare PCB, seems to take the heat quite well. Now I should see if it adheres in between traces and to the PCB substrate of an etched board.