Is the population in Milan large enough to support new businesses?

It really depends on what sort of establishment you'd be opening; as with all business models, there has to be a market for what it is you're selling. Milan does have a small handful of restaurants and some inns around town, so that sort of thing could perhaps do alright here because there's a proven market for it to some extent. There aren't too many, and it's probably for a reason, so keep that in mind.

The population of Milan is not large, maybe 2,300 people, and a lot of them are spread out. The local economy is not very big, at least from what I can tell, but I think the right kind of business could succeed. Tourism (an inn, antique shop, etc.) seems like something that could be tapped up here, as there's enough traffic coming through on the Taconic to be able to draw interest.