I think you should try to cancel your trip until you can get the majority of the above mentioned tests done, and the results.
You first mentioned that the first cytology on the effusion was almost pink fluid, and there was blood present. Again, could have been improper insertion technique or something else, but that certainly does NOT indicate solely, FIP, since the effusive FIP is usually yellowish (sometimes clear). The ultimate plan would be to get a new sample of effusion (if possible) and send it off to a lab to do the cytology, just in case the vet didn't really know what he was looking at the first time. But, as your NYC vet said, if there is little fluid to get, one should not attempt to get it because it could in fact, cause a collapsed lung, or even cause damage in the pleural space, (introducing bacteria, air, etc). In that case, the ultrasound guide could help determine IF there is enough fluid to collect.
Otherwise, see if you can ask the NYC vet about what tests can be achieved with blood or serum. For that matter, ask if the ultrasound guided fluid tap is even a good idea right now, and see what he says about blood or blood serum collection only.
The goal is to rule out FIP, but also to rule out other problems that are possibly mimicking FIP, which happens alot with vets who don't know what they are doing, or when they forego additional tests based on their crazy assumptions. Again, any advice/plan you can get out of the NYC vet would be ideal. I realize you said he was swamped, and for what reasons I do not know, but you have to have a vet who knows what plan of action in testing is prudent right now, the availability of those tests and fast results, and how to address this immediately.
Cat liver issues
Re: Cat liver issues
..........Traci