Since the Guitarra Portuguesa has six courses, (12 strings, in pairs) you could easily tune a regular guitar to the same tuning to try it out. I have the tuning written down somewhere, but it's probably on the web too. I seem to remember it had the top three strings repeated on the bottom three, but a few frets down. You may need to change the string gauges, and considering the nature of Fado music, you might want to go light, to help achieve that liquid sound. Once you've tried it and found the right gauges, you could get a 12 string guitar and continue your transition, until you're ready to lay down the dough for a real Guitarra!
Boa sorte! Espero ouvi-lo tocar, um dia.