Q: How many job search sites are too many to check?
A: As you sense, time can be misspent looking at unlimited job search sites. Key amalgamator sites, such as Indeed.com or Idealist.org are important, depending on the focus of your search. Specialty sector sites such as goinhouse.com or usajobs.gov are worthwhile, as is signing up for job alerts from practice-specific LinkedIn groups you can join or through a (free) service such as ChronicleVitae.com (if, for example, you are interested in a range of higher ed jobs (including university legal work, teaching, and administrating) .
Try a number of sites and see which you find most fruitful. Just don’t spend undue time covering the same ground on multiple sites.