You've given me a lot to think about, thank you. I suppose I've always romanticized Explorators a bit. From what I've read of them, they always seemed somewhat a law into themselves, a driving personality much like a Rogue Trader going forth for science and exploration. It always seemed so lovely, to find and recover what was lost. Then again I suppose that would lead to finding things that should not be found, yes?
It is a lovely thought, but remember this is GRIMDARK(tm). NO FUN ALLOWED.
XD But all jest aside. If you want to see an Explorator fleet in action, you might read the Forges of Mars trilogy by Graham McNeill. It follows an Archmagos who’s lost essentially everything and is embarking on an Explorator voyage to hold onto some of his power and authority. It also features a Titan legio, Cadians, a rogue trader and his crew, menials and their struggle on a Mechanicus ship, Black Templars, Eldar, and AIs. So you get a little bit of everyone’s perspectives on an Explorator fleet. I really enjoyed the book, though if you want to keep some happy closure I recommend skipping like... the last two pages. I screamed for days.
If you’re looking for quirky priests though, you can definitely have that. There was quirk all over Forges of Mars and the Horus Heresy series ‘Mechanicum’ (Which I also tremendously enjoyed and you can read separately from the Horus Heresy series- just a basic knowledge of the Heresy timeline/lore is plenty to get the gist of the greater events.)
And plenty of priests sin, according to their dogma. Most of the upper echelon I would argue sins. It’s just that some are better than others explaining it away, justifying it, hiding it, killing those who are a threat to them, and/or surrounding themselves with other like-minded priests. You can get away with a lot when you’re in some remote location with a handful of other people just like you. Sometimes leaving a broken cog is more practical than going to the effort to replace it. So if you want a priest who breaks the status quo, you can, but part of their story is going to have to be how they broke from the dogma and how they deal with the potential back-lash of not fitting the mold. It’s a tale as old as time.