Is it dangerous to get blood work done too often? what constitutes as "too often"?

Depends on details: Sick people in the hospital sometimes get blood tests several times an hour. Some people in the outpatient setting have lab tests that require several samples over a few hours, such as blood sugar testing after drinking a special sugar drink. Compare that with some very healthy people who get blood tests only a few times each decade. "How much is appropriate" is whatever is medically necessary.