Start when ready--soil is not frozen. You may need knobby tires and chains as there is still 14 inches of snow around here.
Be sure to include seed as an optional extra--improve results and make each job a bit more profitable. Be sure to include starter fertilizer to improve results and add a few dollars more to your income. Soil test and lime are another possibility.
For best results you need a steady source of income in addition to power raking and aeration.