List makes sense for practical purposes, especially since this is a tabletop game, though, I think you'd want some kind of sample to ensure that the players that join are up to snuff and not just random people who wandered in from the Free Roleplay section.

Regarding Spectres, having at least one Spectre would be good so that we could theoretically go wherever we want and act with that Spectre's authority, e.g. Noveria in the canon. Having none would be interesting since a non-Spectre group would have to work within the confines of local law and be somewhat restricted to what it's legally allowed to do, allowing for some interesting choices and plot developments.

I have no opinion either way, however, though it should also be said that whoever is the Spectre would probably be the leader of the team.