So at least two, maybe three or four assassins on Malum. With just the Vindicare I guessed he was tasked with protecting the inquisitor, but with multiple I doubt that's the main mission, at most it'd be a side objective or something the Vindicare did on his own initiative (keeping inquisitors alive is usually a good idea) because he was in the area and it didn't endanger the mission.
I do think Tide should've gone full mask off the moment the Callidus went mask off. Since Assassins wear sealed armour/suits, the only way to infect them would probably be to physically get through the armour, like say using a swarm of Infection Forms.
Though maybe Tide didn't go fully mask off like that because he didn't want to fully establish himself as hostile to them? As the original goal/motive was to just find "Sulla" and ask her some questions.
Speaking of Sulla, if the real "Sulla" is dead (presumably by the Callidus to steal her appearance as a disguise) then unfortunately the real Orion will be getting some bad news. Another Tide therapy scene?
A psychic scream killed the tarot card reader? Betting that's when the Flood arrived.
It's the most derivative, cliche, and plagiarism filled 2 hour spectacle ever seen and no one who sees it ever realizes this because the only people still alive who have seen the sources of the stolen material are either busy silently screaming as a skeleton on a throne or busy maintaining a massive museum (also as a skeleton).
I can definitely see Big E, Malcador, Trazyn and Perpetuals (in general) making constant references. Hell, the Astartes legions and much of the Imperium is just one big Roman Empire reference (Legionnaires, Centurions, etc).
If the Halo franchise existed in the 40k universe, Big E will probably recognise exactly what the Flood is but also kinda freak out at the fact it's somehow real. Possible premise for a TTS omake? Big E either meets Tide or finds out what's going on at Malum and freaks out while everyone else is confused. Except maybe Magnus who actually gets the references due to his extensive research and curiosity about what in the Warp, Big E and Malcador were (still "are" for Emps) constantly referencing.