All of the campaign traits from the players guide give reasons for being in Sandpoint - that's what they're for. That said, there's no reason those traits can't be worked into the idea of an established band.
For example, Marcas' trait gives him access to a "ruthless thug" in Sandpoint's shadier side. If the group heard about the troubles there and decided to investigate, Marcas would volunteer that bit of his background and suggest that Jubrayl might know what's going on and be willing to share some information.
I like this approach, airwalkrr. We get right into the action this way, and if we remember to do it we can drop little tidbits of our backstory into the game and develop that in parallel with the AP plot rather than piling it all on the front end as a way of getting the party together.
[sblock=Preliminary Background]Still a work in progress, but here's what I've got so far in case another party member or two wants to develop some details of how we initially hooked up.
Marcas is a Shaonti (of the Lyrune-Quah, the Moon Clan) by birth, but was lost to his tribe somehow. He was found and adopted by a Szarni family. As he grew up he found that his life as a Szarni did not sit well with him - his nature was more ordered than theirs, and some of their less benevolent leanings were distressful. When he reached his adulthood he left to find his tribe and "discover his roots." He found them, and lived among them for a time. But though he learned their life, and even took their tribal tattoos, he didn't really belong there either. He left them as well to continue his search. He came to a monastery and their simple way of life called to him . . . at least more so than either of his previous 'lives' had. He spent a few years with them as well, "getting in touch with his spiritual side," learning a little about how to harness his Qi, and learning the Way of the Bow. The monks there believe in using one's abilities to do good in the world, and so when they declared him ready he left their sheltered walls to do just that. Along the way he met with various and sundry adventurers whose talents and goals complemented his own. And there we find ourselves . . .
(A little stereotypical in places, I know, but it serves. Also, from this it looks like I'll be starting out Lawful Good rather than Lawful Neutral. This works well for me, as the shift from there to Neutral Good isn't as extreme and could happen easily. The more time he spends away from the monastery and in the company of those whose lives are more, um, messy(?) the more he loses the discipline that he learned there. Also, some of his Shaonti blood and his Szarni upbringing can come back to the forefront.)[/sblock]