Originally posted by Jed
Depending on how you choose to interpret this reply, it's either a lot of help or absolutely no help whatsoever.
Let's start with the simple. Film. No, on second thoughts, that's not simple either. Certainly stick with something in the ISO 400 to 800 range. And stick to Fuji as a general rule, and you'll be alright.
Now here's the tricky part. I considered your problem and then the answer I came up with was, I'd look at the shooting conditions and then make my decisions. I'd decide between ISO 400 and ISO 800 based on the amount of ambient light, the height of the ceiling, the client's reproduction needs, how rapidly I might need to shoot with a view towards flash recycling time, the colour of the ambient light, the colour of the ceiling and walls, the presence of reflective surfaces such as mirrors, the focal lengths I will be shooting with most of the time, the aperture I would need for the majority of the shots.
Put another way, this is all stuff that I haven't thought about at all, just wrote down as it came to me, because it's stuff I apply automatically when I shoot in a new environment. Quite probably I've missed several factors out as well. Crystalised I supposed you could boil it down to one word; experience, but here's where my bit about being able to interpret this two ways. In the negative manner, this could be some poor sod trying to show off his apparent experience and has really told me absolutely nothing that I want to know. On the other hand, my positive input would be for you to shoot, and learn from your mistakes. Copy that list down and use that as a checklist if necessary. I know I haven't provided the answers, but the answers aren't ever clear cut. There's no magic formula because conditions are forever slightly different, and it comes through experience and practice that you'll be able to look at a situation and determine what the best things to do and use will be; where to make your tradeoffs and sacrifices.
Good luck, and good shooting. And if you have more specific questions, I promise to be less cryptic in future.