1) Probably dropped anchor there, wouldn't have gone further than the waterfront taverns that his fellow sailors had gone to, so he can drink and gamble with them (probably sailors from other ships to avoid any hard feelings following a streak of luck). Unlikely to have actually met any locals aside from wenches in the taverns. Wouldn't have been on the actual island, or out of sight of the sea even.
2) I'm thinking we sneak there cross country, avoiding the villages etc. and sleeping in the outdoors - this depends on any info we get on the set-up of the country and these patrols (i.e. is there a curfew, are people confined to their villages, can you travel without a permit, do these patrols generally patrol the countryside or the villages to maintain order). Not sure where this info would come from, but if thorn's been there he might know.
We'll presumably need to come to a party consensus on that one though
3) Well, my plan was rock up at the Baron's door and say something like "You wanted to see us sir?" Given that we would then be in his custody basically the ball would be in his court to throw us in prison or interrogate us or whatever he wanted. If he denied knowledge of the attempt to capture us I guess we explain what happened in private and suggest he has some kind of not-quite-a-traitor in his midst, given the specific instructions of our capture.
4) Given that they are probably his unfleshed patrols, I was planning on asking the Baron how to deal with the poison when we met him