In terms of lower taxes and what you're seeking in terms of newer home construction, I find myself directing families to Armonk -- only 25 minutes from Tarrytown.
As for schools, the following link to School Reports should provide you with some helpful information -- http://www.houlihanlawrence.com/schools.html
My wife and I are relocating in May to Southern California - due to my new job. We've enjoyed living in the Half Moon Bay community in Croton on Hudson (right on the water) and know the schools in this district are good. Croton is about 15-20min down 9 to Tarrytown.
We are selling our townhome at HMB, feel free to check it out. We are next to the Croton-Harmon train station with a 40min commute to NYC. Very convenient.
Good luck with your search!
I was born and raised in Westchester County so I would be glad to help. Most of the county has fairly high taxes especially the ones with the better school districts. Pleasantville might be a good place for you to look. It is close to the taconic, quiet, with decent schools. I do have a lot of brand new pre-foreclosures in Westchester county if you are interested. Contact me for more info!