Compared to the rest of the Fairfield market, the Greenwich submarket has more expensive rates, and you'll have to negotiate above asking rent to be in this hot region.
In the last 90 days, 36 listings have come on the market, which means new listings most likley are leasing quickly. You'll want to be prepared to make an offer immediately. About 6% of the listings in the Greenwich are subleases, so you will probably have to focus your search on direct office leases. There aren't many listings below 2,000 square feet posted, so finding a space for a small business might be tough.
The standard measurement for office space in this area is around 2,000 sqft. Most buildings in this region are around 3 stories. Most buildings in this region were built in 1972 and are Class A.