Oxford Bibliographies offers peer-reviewed annotated bibliographies on specific topics across varied subject areas. Each of these features an introduction to the topic. Bibliographies are browseable by subject area and keyword searchable. For research in early America, the Atlantic History module may be particularly helpful, but, depending on your research topic, any number of other modules may provide leads for your work, too.
Different modules may offer articles on the same topic, as with, for instance, settler colonialism:
Link to the general collections of Cambridge University Press, including the Cambridge Histories and Cambridge Companions. A few examples of titles of potential interest are:
A large collection of resources. The Wiley Companions will be especially useful. Navigate to "Humanities" and then "History" in order to find a detailed listing of titles available for U.S. history (also covers other parts of the world).
In addition to online library catalogs, reference sources, and footnotes in sources you've already found (etc.), subject-specific databases are another extremely helpful resource for finding secondary literature, including the latest scholarly journal articles in the field, and a key one for researching U.S. history including early America is:
Searching America: History and Life will allow you to check for the latest scholarly articles, reviews of books, citations to book chapters, and more in historical journals such as The William and Mary Quarterly, Journal of the Early Republic, and Journal of American History.