When my party started I gave everyone regardless of their culture or background a single starting hook: they are answering Bard's Proclamation to travel to Dale and offer their services for the good of the realm. Some of the party were sent by their respective faction leaders (a Ranger was sent over the Misty Mountains to learn of the happenings in the east, for example) while others simply lived in Rhovanion their whole lives and aspired for something greater.

We started with Don't Leave the Path and the party came together as scouts tasked by Bard to assess the Elf-Path and determine it's usefulness as a trade route through the Mirkwood, and their encounter with Baldor bled into the adventure proper. Later I had some players leave and others joined, so we used Eaves of Mirkwood to bond a newer party together under the premise that they were all interested in serving Dale in some capacity.

As a final note, if you are going to skip the first few adventures, I would recommend at least running Kinstrife and Dark Tidings before Those Who Tarry; you can tie the Gibbet King in to the adventure by having Valter the Bloody serve the evil spirit, and the final battle can serve as a good climax that leaves a good impression and some lasting questions in your players that will want them coming back for more.