If you sell anything important, you can buy it back again in the evenings from the trader's tent in the town.
And there is generally no time limit on any actions. You can't really "miss" anything. Just keep interacting with the same person until you trigger the events that progress the story. Some events have to happen before others become available.
Check out the character pages on the wiki (see the game's home page, linked above) for some details on their progress paths.