I was there in 1999, so plenty could have changed since then, but my advice is:
1) your practice falls to you. If you spent that much time on retreat you should know how to do it. Sensate reality with as much precision and inclusiveness and consistency as you can manage is the key. Read Tarin's Reformed Slacker's Guide on the Wiki if you need inspiration.
2) Gaia house is absolutely beautiful, the food when I was there was great, and the people were quite nice: again, this was a while ago, but hopefully they have maintained those aspects.
3) Teachers came and went when I was there. Do you have one set of teachers for the 90-day? There are so many styles of practice, and realize that the Mahasi style is very strong in map theory, technique and the like and this contrasts with the emphases and strength of other approaches and teachers' perspectives and realize that you may all feel like you are doing insight practices but might feel like you are speaking completely different languages regarding how you describe it, conceptualize it, and even what you feel it all leads to. This can be frustrating, so try to learn what they have to teach on their own terms, and it will work out better. Try to translate into their language and paradigm when possible and it will make for better interactions. Goal oriented, hardcore practice is not for everyone, and that paradigm is not the norm in the West at all, so coming from a Mahasi place, where gunning for stream entry and beyond is considered normal, to a place where people might be all about their back pain and issues and their spiritual trip may be a bit of a shock, so just ignore that, and try to get what wisdom you can out of the experience, as if you get caught up in the differences between trips it can really interfere with gaining what you might otherwise be able to.
Best of luck!
Daniel
