In the last 90 days, 1 listings have been made available, which means new availabilities most likley are leasing quickly. You'll want to be prepared to tour spaces as quick as possible. About 100% of the listings in the Cos Cob are subleases, so you might be able to sign a shorter term by taking over a previous lease. 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 sqft. Most buildings in this market are close to 3 floors. Most buildings in this region were built in 1967 and are Class A.