I support the mini-campaign idea, I would also suggest this idea I found in Dragon magazine. It suggests to set up your campaign as if it were a TV series; create short, easily-solvable adventures that could be finished in one sitting or two, and somehow string in an occassional over-arcing theme that reocurrs throught the campaign. In this way, there's not too much pressure on you to create "The Big Story" all at once, and it gives the PC's a sense of immediate satisfaction.
Also, get your group together and discuss making a "themed" team - a team that actually has a point to work together, complements each other's skills, has a clearly defined "role", and to agree upon not stepping on each other's toes. A group that is a madcap collection of classes, races, PrC's and variant rules just isn't a cohesive "cast".