So, I notice that the GMing chapter seems to suggest that one player as inquisitor is the default, with none a backup plan and multiple inquisitors a special scenario.

Has anyone playtested the different Inquisitorial arrangements? I know in Dark Heresy, it was heresy to suggest that the ][ even appear more than once every few sessions, but the Beta seems to feel that the acolytes should work more closely with their ][.

I've kept to the old theme, the party are currently working for a interrogator. I currently have them dealing with the fall out of their previous characters' actions. It would be in testing to see how one of them handled being the inquisitor, but i imagine it would end up with the whole sector being picked clean by exterminatus.

Depends on how your group likes to play. If they're a Rogue Tradery sort, working with the inquisitor closely Ravenor/Eisenhorn style could be pretty useful.

If they're a Cthulhuy sort, you can easily send them into the horrors of the 41st millennium with only a few cryptic letters.

Having an inquisitor in the party tends to give players more of a feel that they're 'in control', and they have some determination in the course of sector events, similar to Rogue Trader. I'd surmise that's why it's the primary recommendation.

For alternate playstyle themes, I'd look at lovecraftian horror books and games for some inspiration, perhaps. A group with no inquisitor may be excellent for a meatgrinder game.

For multiple inquisitors, you could certainly do it. But that's mainly the GMs understanding of how the lore dynamics work to make it more enjoyable:

You could have them both acting as if they were the same inquisitor for an intrigue campaign.

Or you could have them acting in a tight ideology-based alliance, using their influences in tandem. (More difficult to avoid splitting the party detrimentally here, though.)

Or you could have them both in a loose alliance of circumstance, each having an oathbound bodyguard or two. (Probably the most difficult, but okay if you like some higher inter-character tension.)