I regret that I have no practical tips to offer, but for sheer inspiration you might take some St Exupery with you (particularly "Southern Mail" and "Wind, Sand and Stars " ), and there is a lavishly illustrated French book featuring Chuck Ellsworth and others flying a similar route in a Catalina. I'm very jealous. I would like one day to fly a similar trip and maybe continue to Dakar.
Others will no doubt chip in with practical help in a bit. Good luck.