Enigma, I've done this a couple of times and it worked out fine for me. Flights from Europe often are very cheap to NYC and you can save hundreds of dollars using this tactic, especially for one-way travel. For going to SEA, it's good if you have an Alaska Airlines Frequent Flier account (Alaska has a hub in SEA). You can go from Newark to SEA spending only 12.5k miles on Alaska Airlines.
Keep in mind that long-haul international flights are almost always on-time as these flights get priority over domestic flights. Domestic flights are more likely to get delayed so give more of a safety buffer for them. Be sure you include plenty of time for going through immigration, getting your baggage and going through security again. Also consider the time of day when you are making your connection. At 11am, the airport might be very busy and lines can be long. One time my second flight was only three hours after my first flight landed, and it worked out, but I suggest you have a larger buffer than that.
Keep in mind that long-haul international flights are almost always on-time as these flights get priority over domestic flights. Domestic flights are more likely to get delayed so give more of a safety buffer for them. Be sure you include plenty of time for going through immigration, getting your baggage and going through security again. Also consider the time of day when you are making your connection. At 11am, the airport might be very busy and lines can be long. One time my second flight was only three hours after my first flight landed, and it worked out, but I suggest you have a larger buffer than that.