We have a lot of compressors of all shapes, sizes and ratings from a few Cfm to 600 cfm in a lot of locations inside & out around th epowerplants. Condensation is a BIG problem. Locating the compressor outdoors will get colder denser air to the intake- upping efficiency. The downside is there will be a great deal of condensation in the crankcase. We have single stage splash lubed compressors on some air circuit breakers out in our powerplant switchyards. These compressors run very intermittently and are in steel "doghouses". Condensation in the crankcases is a real problem, so we run electric space heaters. These are three phase motors, so we ordered them as drip-proof, with internal electric space heaters to keep the winding warm. We also keep a 100 watt bulb going in each of the compressor doghouses.
Another thing you might want to consider is an automatic condensate drain for the air receiver tank. Most compressors use a "syphon" pipe which dips from a connection at 3:00 or 9:00 on the receiver down to the bottom, putting the receiver drain valve on the side of the receiver. This often leaves a little accumulation of condensate in the bottom of the receiver. I have had compressor recevier drains changed to come right off the bottom tapping, and had the receivers mounted with alittle pitch to them to be sure condensate gets drained when the auto drain valves pulse open. On outdoor compressor sin our switchyards, we have had a number of receiver perforate because of improper condensate drainage.
If I were to put the compressor outdoors, I would build a doghouse for it, and insulate it. This will also quiet things down so your neighbors don;t hear much of it. Put the compressor up on blocks and be sure to pitch the receiver to its low point drain. Put some sort of heat in the doghouse- whether it is a light bulb or more. You might ask Eaton, since they seem like a vendor willing to work with the compressor buyers- about some sort of strip heater for the compressor crankcase. On some compressors, even in the powerplant, there is enough of a swing in ambient temperatures and irregualr cycling times of the compressors to cause condesnation in the crankcases. These are bigger I-R recips of about 25 cfm and 350 psig discharge. The local I-R dealer had an actual crankcase immersion heater that went in thru a spare drain tapping for the purpose. It works with an overtemperature thermostat and with a relay to take it out when the compressor runs. If you go to a place like Tractor Supply, you should be able to find a magnetic mount heater that is used on tractor and truck oil pans for cold weather. These are fairly low wattage. With an iron crankcase compressor, a magneitc mount heater such as farmers use on tractor oil sumps should work for you. I note you live in NYC, so if you come upstate to ski, there are Tractor Supply stores in plac es like Marlborough NY (Ulster County) and Oneonta, NY.
Other concerns about mounting a compressor in a doghouse with heat: rodents. Build a warm compressor doghouse and you will have critters occupying it. Critters love to build nests out of fiberglass insulation in and around equipment. They also love to chew on wires. Even common field mice (or house mice) will do a lot of damage. Ask if the motor you get has screened ventilation openings and run any wiring in conduit or "sealtite flex". If you use rigid foam insulating board you will lessen the chances of the critters making off with it and building nests in places like the belt guard or next to the warm crankcase.
Another thought: I do not know how close your nearest neighbor is from your proposed compressor location. A bvelt driven compressor with disc valves is fairly quiet but does have a distinctive sound. If you have an automatic tank condensate drain, a lot of these simply work on a timer plus a time delay realy to give a short pulesed opening of the receiver drain valve. This causes the receiver pressure to drop off. After a few days of the receiver drain cycling, the compressor will cut in whenever the pressure drips to the cut-in pressure on the pressure switch. Could be any hour day or night. Or, you might simply be burning the midnight oil in your shop and using air, so the compressor cuts in at some late hour. You might want to ask about an intake air filter/silencer. This is an overgrown air intake filter and tends to dampen the pulsations and reverberations the intake air makes- which is a lot of the compressor noise.
Joe Michaels