Yes. You use that function maybe if an order comes up that requires that particular item and you want to restock it. Otherwise you just have to wait to make a sale (by fellow gamers) and as stated above eventually Wesley will take it. Doesn't usually go over a day before it disappears.

Also tradefest

Be patient.

Yes

The potions come from the big purple octopus, occasionally from the treasure chest hermit or purchase at world market

Sometimes they dont show for a number of levels.

The maps are just items that you collect in order to open up other islands. Collect them and when you are able to access the other islands feature (dpending on what level youre on and whether youve cleared the part of your island that reveals that feature - i think it is beside the stone bridge to the right). The maps "pay" for access to each island. I.e. you need to collect a certain amount of different maps to open each island. Always keep blue and white maps as they are the rarest and red ones are second rarest. Collecting maps can take up valuable storage. Also islands will appear out of nowhere based on levels. Dont sell all of your maps, especially rare maps, after you think youve opened all maps.