This is basically a resort on a pleasure world. Two of the Acolytes are nobleborns, so in a four person party, it will be fairly easy for the two nobleborns to fit in, and the two non-nobleborns to pose as their bodyguards (in fact the Inquisitor will suggest this to them).
Is there somebody else who seems to be looking for something?
Yes, actually. The reason the Inquisitor is there, is because he's learned there's going to be an assassination attempt on someone he believes to be an important lead, and is there in person, to try and catch the assassin in the act (that way he gets two sources of information instead of just one!)
Is there someone in heavy armor, with expensive gear/clothing or something else that screams "Inquisitor"
Most of the individuals the Acolytes will be meeting here are nobleborn, so yeah, a lot will be wearing expensive clothing. The Inquisitor will have placed two of his Acolytes there as well-- one dressed to stand out (basically wearing rags to a gathering like this) and the other in full military dress. There will also be a Rogue Trader that the Inquisitor has worked with in the past, who may be able to point the Acolytes in the right direction (though is just as likely toy with them awhile first, especially if they mistake him for the Inquisitor!)
Is there somebody who seems to have an eye on me?
Oh yes. At least two individuals there (not including the Inquisitor and his retinue) will be taking an interest in the Acolytes, one of them being the assassin the Inquisitor is there to deal with. As I mentioned, the Big Bad of this campaign is an Eldar. And one of the great things about having an Eldar as the villain of a campaign is Eldar have that terrifying foresight that can let them see threats coming and put measures in place to deal with those threats.
Is there someone people don't know?
Somehow I didn't consider this. I do like the idea though! Will have to find a way to implement this, as there would likely be some regulars to whom some of the people (The Inquisitor, the Rogue Trader, the assassin and the Inquisitor's Acolytes) will be new.
As for the size of the thing, it's not gonna be huge, but it's not gonna be small. 20-30 people probably, a lot of them "faceless". I'll probably only focus any attention on perhaps about a dozen of the people there, the Inquisitor, obviously being one of them.