So obviously they would be limited to coastal areas or maybe rivers, but in general, how far could the Vikings go down East Coast if they wanted to, and what could have motivated them to colonize there?
You could end with more settlements in America, but they would be limited demographically, and vulnerable to native attacks and/or absorbtion, due to a lack of real motivation to have a reasonably important (demographically wise) move of population.
There is evidence that the Vikings got as far as Arkansas. There has been speculation that Viking explorers may have gone as far as Wisconsin and Minnesota . Viking coins have been discovered as far west as Oregon but there is no positive proof.